Hi, This is some thing very strange means I have never seen such type of behaviour. Anyways try it this way like Uninstall these new AJAX software.
Check whether now other templates are visible or not . If not then only way left will be install your .Net again.
The procedure to install AJAX is like first you install ASPAJAXExtSetup and then ASPAJAXCTP.
This is what i suggest you should do if you will find some other better option then please go ahead.
One more thing its not necessary to use the template to start AJAX Enabled application you can do the same by just changing your web.config.