My hard drives have disappeared

hi,

my computer shows no hard drives partition except one and if i try to access them using the run command i get "this folder does not have a program associated with it
for performing this action create an association in the folder options control panel".
but i can access them using rounds about like "c:\windows" etc. my start menus shows no programs and i cannot access the folders on my desktop. every time i access my anti-virus i get "avcenter.exe has encountered a problem and needs to close" though the related process seem to be running. i restarted the computer in safe mode and ran the anti-virus program. it picked up a couple of virus but it has not solved my problem. Please Help Me.

OS: windows xp
Anti-virus : avira
 
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