On my machine i have a virus . It is really odd and i have no idea to get rid of it.

I don't know how i got it but yesterday evening my machine was fine, come up here this morning and have the virus. I downloaded nothing overnight and only used 3meg net usage (SOB) so it is unlikely to have downloaded either.

I cannot do much on my machine, it boots up ok but then someone/something has control over it. I could not type a message to post on here as the browesr (both IE and firefox) continually refreshed, couldn't do AVG update as it closed it etc. Just now it even shut my machine down !!!!
Since then i have taken it of the network and internet so nothing else can get in or out, i managed to update AVG by opening word and after kicking off a scan switching windows - but 2 pages worth of text ( y's and 6's only) have alreayd been typed. I unplugged ps2 cable and removed batteries from my keyboard but it still happens - therefore it must be installed code rather than control.

What should i try ??