winmm.dll corrupt or missing

I just turned on my pc and my anti-virus (Avg Free) isnt working correctly (Resident Shield, and e-mail scanner not active) and windows security alert poped up on my taskbar.

I tryied to run winamp and the theres and error with the winmm.dll and advises me to run chkdsk. i did but still the same ballon pops up everytime i open winamp, also i opened notepad and another ballon pops up saying the might be a problem with notepad.exe...

i tried to run a virus scan but it doesnt start.. what should i do?

thanks

 

oh i forgot to mention that i can use all applications normally, winamp, notepad, explorer.. etc.. except the anti-virus

 

I dont think lack of ram was the issue, mine is 512MB.

Anyway, when i got the problem i started back-up of all my files and got a number of different messages: 'winmm.dll is corrupt and unreadable' and also for winrnr.dll and wintrust.dll

Ran chkdsk and restarted the computer and got the BSOD which stated 'STOP: c0000135 (unable to locate component) This application has failed to start because winserv was not found'

I end up formating my disk because my pc was becoming really slow and i was experiencing some above normal boot time (8 mins or something). now its around 1 min. Anyway problem solved, but still would like to know what could have caused that.. virus?

Im using XP SP3.
Cheers

 

I don't know if this is same problem, I ran a scan earlier-avg and nothing was found, but then my laptop started freezing and going slow, so I restarted and when it started up I got a black screen and message - this application has failed to start because WINMM.dl was not found. Re-installing the application may fix this problem.
I press ok and it keeps coming up for each program, I inlay managed to get laptop started up in safe mode and nothing works,
I cannot run avg I get same message, I can't start Internet, my wifi icon he network cons down right bottom screen are gone. Everything I try one just brings up same message.
I looked into why to do but all I find is re install or download new one but I can't get on Internet on my laptop so I'm stuck?
Can. Fix this at home or is this a pro job? And any guesse why may of caused it?
Sorry I it's off topic, new to this site