vista wont boot past the welcome logo

hi all i have done all the diagnostics and they seem fine but pc will not boot past the windows vista welcome page can any1 help me

Does it just freeze?
Get a message or blue screen?

no the refresh circle continues to rotate

Try to boot into safe mode.
http://www.vistax64.com/tutorials/123496-safe-mode.html
In safe mode try a system restore from before the problem.
http://www.vistax64.com/tutorials/76905-system-restore-how.html

If that does not work, in safe mode, set up a clean boot and see it that helps.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7

The circle is a symptom of freezing.