I've heard of some viruses disabling access to regedit, as well as other utilities.
 
Might want to have a scan with Stinger and Housecall just to make sure you're really clean.

Does the shell make a difference? If you cant start the process from START / RUN and you start regedit from CMD.EXE
 
Have you been playing with local policies on the machine?
 
Can you access your registry with a 3rd party tool?
http://www.resplendence.com/reglite
 
Besides running a fully updated AV, I would also run adaware and spybot.

Hi I had a friend over last night and he brought sum1 with him, the guy knew alot about computer and when i woke up this morning i cant see any of my drives (runnung xp-sp2 btw) cant see the shutdown computer buton in start menu, cant see run in start menu, cant acces any drives by just typing in the drive letter i get "access to the resource"c" has been disabled" although i can get around each of these things i would rather have them on my comp because i prefer getting around fast. thx

solution here http://www.softheap.com/restrictions/hide_drives_in_my_computer_002a.html
 
nvm