try this free online and secure scanner. I have used them for years to find tough cases for me.

Trend Micro HouseCall - Free Online Virus and Spyware Scan - Trend Micro USA

click on the Scan Now. It's Free!

Note******
It is best that when running this scan to have system restore turned off in XP

R.clk "my computer" click properties > system restore tab > tick the "turn off system restore " box.

The bad guys just like to hang out in the protection of system restore folders and files.
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As for the other ailments...you will need the XP installation disc ( not a restore disc)

Start > run and type

sfc /scannow

(notice the space) press ok and the system file checker will replace all system files back in their original condition...

On some computers this works without the CD so try it all it will do is ask for the cd if it is needed!