Serious windows problem

[sunny_4u]

install norton antivirus and update it...

 

[pkjha30]

rundll32.exe is system programme for windows xp. rundll.exe in your system is most likely infected trojan , assuming that you are running windows xp sp2 . Registry entry might have been repaired because of system restore, but as someone said, file will still be there and might cause damage to system later.
If possible run scandisk at boot time.
Run sfc /Scannow

What you can do additionally is to run HijactThis(HJT) and post log file on tech support fora. They will be specialist in helping you out.

http://www.techsupportforum.com/
http://hjt.networktechs.com/
these are two such fora.There are many more such excellent support fora.Just call for help and they will help you.

Don't get spooked by horror stories listed there.

pk

 

[imcool]

just take a backup format and reinstall windows and then use a original copy of any antivirus software