Problem in Windows 7

[LucidOnion]

Recently I've downloaded of what I thought was an mp3 to my computer which runs Windows 7. I thought it was harmless, but apparently not. When I fired up my computer the following day, the startup was unusually slow, and upon the start a message popped up. "csrss.exe has stopped working" which was followed up by: "Steam.exe has stopped working" "AIM.exe has stopped working" and "iTunesHelper.exe has stopped working" My Internet was (and still isn't) working, not picking up my wireless signal. (Router and signal is fine with my laptop) and the software for my PC wireless adapter card wouldn't work. I used AVG to scan for any viruses or trojans causing this, but nothing came up druing the scan. I would appreciate ANY help from you guys, because it is surely needed. Regards, Onion Edit: The driver for my adapter is gone, and won't re-install correctly. Please help.