What color is the Firefox button in the upper-left corner of Firefox?
Purple means you're in Private Browsing mode, and Orange means you aren't.

If neither Start Private Browsing or Stop Private Browsing appear in the Firefox button drop-down (or Tools menu), you probably have the Disable Private Browsing extension installed. You can't see that extension in the Add-ons Manager tab, unless you open Firefox in the Firefox SafeMode.
http://support.mozilla.com/en-US/kb/Safe+Mode

Cannot Uninstall an Add-on

• https://support.mozilla.com/en-US/kb/Cannot%20uninstall%20an%20add-on

Check and tell if its working.

You can see that Disable Private Browsing extension listed on the Help > Troubleshooting Information page if it is installed. If the extension is working (and the missing PB menu entries would confirm that) then you can't enter Private Browsing mode.

This extension disables Private Browsing, hides all the PB menu items and disables the keyboard controls, disables the clearing of browsing history, and the extension doesn't appear in the Add-ons tab except for in the Firefox SafeMode. It also renders the Troubleshooting Information tab blank for Extensions, Modified Preferences, and the Graphics areas on that page. In SafeMode all that information does appear.
https://addons.mozilla.org/en-US/firefox/addon/disable-private-browsing/

Thanks everyone for your replies. It's been educational.... I went into safe mode and I was able to get everything working through there. Learn something new everyday,,, again thank you for your help! :)