PC with XP pauses at Logo screen on boo...

It's a Compaq Presario SR1517CL Desktop running XP. I have installed all updates, etc. as of June. It has been stopping at the Win Logo on start up and pausing there (no activity on the hard drive light). If I turn it off and start again it usually starts normally after a few tries, but it's been getting worse. Now, I can't get it past the logo screen at all.
It starts in safe mode. Irun Fix-It Utilities to scan the reguistry etc. on a regular basis.
Any thoughts? Is there a recommended diagnostic program worth getting?