explorer.exe not working

[Hair|Trigger]

I've got an old comp in my room with XP SP2 (I think), recently I got it fixed up (upgraded to 512MB ram) to make it useable, but for some reason explorer.exe refuses to start.

I can run it from task manager but the tskbar pops up for a split second and dissapears, so I can only launch programs from taskmanager >.>, no icons on desktop or start bar at all.  just shows the wallpaper

ideas?

EDIT:  Are there any applications that need to be running for explorer to work?  because I launched google desktop and then tried explorer and it's working, with net and all.  even after reboot D: 

[PANZERCATWAGON]

you may have to repair your operating system with your xp boot disk

[Hair|Trigger]

I tried, but it asks me for a password and I don't know what it is -.-

and the disc is actually for an ancient Compaq laptop, and my computer is an ancient Packard Bell desktop, so I dont really wanna mess it up or anything (I'm running the laptop's os on my desktop though)

[DarkNoddy]

I'm not a huge fan of system restore (dont use it myself) but if this happend recently you might give that a shot.
Might be you have some spyware on your computer, have you scanned for any? You can run HijackThis (this is not a spyware finder, so dont remove stuff unless you know what you're doing.) and upload the log so someone can have a look at it.

About your Edit, you can run explorer fine AFTER you ran google desktop?

Also you could check out the event logs: run eventvwr to get it open, start explorer, note the time, and check application / system for any errors at the time you started explorer / booted up.

[Hair|Trigger]

I tried, explorer shows 0 events (nothing to view)

if it happens again I will try it though, thanks