Major problems

I have been attacked by a virus which has created some major problems on my computer which I cannot remove. Here are the problems that I aam having:

Try to open desktop ICONS and I get a message that "this file doesn not have a program associated with it for performing this action. Create an association in the fil options control panel" I get this on every program I try to open an then I have to right click on the program got to "run with" and then unprotect my computer for the program to open.

Also my computer cannot open file rundll32.exe. Last I have "backoor.???" trojan virus which is continuously picked up by my default virus scan but after reboot is not removed..

I have used the follwonig programs to try and correct the problem:

Spybot / ad-aware7.0/ Yahoo tool bar anti-spy/ registry mechanic6.0/

I also ran in dos the sfc/scannow option. I am out of ideas!!!! please help!

Danny