To diagnose problems with Thunderbird, try one of the following:

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Thanks Matt, I didn't realise that I had Add ons running in the system, even after looking at the add- ons I still couldn't locate which one was active and probably causing the problem. Anyway Restarting the thunderbird program now seems to open in about 10 seconds instead of 1 minute. Anyway if the slowness returns I'll know what to do, thanks. With the other suggestion, re restarting the computer in 'safe' mode, I'll hold off on this as I have been dealing with AVG and their PC tune up program, today they did a complete system analysis whatever that is? and will hopefully get back to me in the near future with reasons why the rest of the system is running slow and their program is not doing what it says. Thanks again.

Having seen Pc tune up programs for the last 20 years. None of them actually work. Most clean the registry and make almost no change there as it is not a cause of much delay.

Most empty the temp folder and undertake a disk cleanup. That is on the start menu under accessories > system tools and has been for about 10 years.

Some undertake disk defragmentation. Actually this can be a huge benefit but really more that a couple of time a year is all that is needed. Again it is in system tools.

Having more than 4Gb of memory is almost required these days and should be considered a minimum for XP SP3 unless you want things to get shakey. Every programs memory consumption rises with each new release.

AVG like most anti virus programs monitors all file opens, read and writes. So basically everything takes longer than it should as the supervisor looks over the programs shoulder.

Have you compacted your Thunderbird folders and provided an exception in AVG for your profile folder. Having AVG so off and scan huge files every few minutes is also something that slows the computer. Hence the exception. Some Thunderbird files will be 1Gb in size. So avg will be busy for about 10 minutes scanning those each time they are updated.

Most importantly watch the hard disk lite on your computer. is it busy most of the time? Usually this indicates swap files use from not enough RAM.

Hi again Matt, again thanks for taking the time to answer my postings. Well, the starting of Thunderbird in record time only lasted a day, alas it's back at it's 1 minute start up time, still with no add-ons running.

Interestingly during the course of writing this I discovered something new. I had as you suggested to disable all my "Add-ons" which I did via the "Add-ons section" > "Never Activate" , presuming this was all there was to it. However clicking on the "Help" button, it gives an option to "Restart with Add-ons disabled" , is there a difference between "Never Activate" and "Add-ons Disabled" ? I presume there must be a difference or this option would not have been given, and also the result was quite remarkable.

So clicking on this option brings up a new window as you would know. The options given are: "Thunderbird is now running in safe mode, which temporarily disables your custom setting, themes and extensions. You can make some or all of these changes permanent: > Disable all add-ons > Reset toolbars and Controls "Make changes and Restart" / " cont. in Safe Mode" / "Exit"

So, I checked just the first option "Disable all add-ons", I didn't check the "Reset toolbars and controls" as yet. The email program opens in under 5 seconds.

So I presume there is a difference between "Never Activate" in the "add-ons section and the "Disable add-ons in this option?

I haven't customised this email program that I know of with the exception of what I have described below, what will happen if I check the "Reset toolbars and controls"? Will I loose anything?

Prior to finding the above solution:

You asked once before if I had "compacted" the files in Thunderbird, I click "yes" each time it prompts me, I have even gone through the individual folders and compacted them to make sure the system was not just compacting the inbox folder.

I have many folders where I try to save individual emails that I want to save in their particular categories. I have created these sub folders behind my email address on the left side. To try to be clear this is how they are. Inbox Drafts Sent Archives Deleted Outbox "My email address" > 20 folders created in here

Should I have created these storage folders in a different area? What is the "Archive" folder intended for? Should I have created my storage folders in that section?  

Could these folders in this section/ location be the cause of the slow opening of the Thunderbird program?

regarding the general slowness of the computer mentioned in a previous post, re AVG PC tune up. As previously mentioned AVG people remotely controlled the computer and did a system check. At this point they have not got back to me with the results of their analysis, in honesty I doubt they will get back to me as they are awaiting the anniversary date to come, which is another week before I'm due to be billed for another year of their so called computer tune up service. As you say most of the program is just a link to tools that are in the accessories of the computer itself anyway.

I haven't ventured down the starting in Safe Mode Option as yet. I sort of understand what you say , from what I understand this gives you the ability to tell the computer to resume to settings from a time known to be 'prior to problems" . However I don't know really when the problems started and to be honest I expect that my limited knowledge in this area would cause more problems than I already have. as the computer works ok, doesn't crash etc, just slow at times, more so with the thunderbird program, perhaps this issue might be solved now.

In stupidity I just wasted 6 hours doing a system back-up over the weekend and I expect that I have just made a copy of whatever problems exist in the system, I will have to remember to do this again if I ever get to the bottom of this "slowness" problem, if ever. 

Anyway, I'll look forward to your reply if you have time regarding the "Thunderbird question component listed above. Many thanks G.