hello friends i had the same problem , firstly my desktop icon was not working.. if i try to open any application a messege always apper ''open with" a list of programm... when i try to open control pannel .. control pannel open but when i try to open add/ remove programm error appear c:\windows\system32\rundll32.exe application not found... . i was trying to solve this problem . i spent lots of time even 4 day. i have tried all the solution provided by this forum but none of these worked 4 me... now i have got solution from this situation . my computer works perfectly... if u have same situation.
try
firstly u scan ur system with a good antiviruse... if this situation apper after xp gurdian 2010 viruse aatack. or xp antiviruse 2010 attack..then download a file" exe file association fix" of 1kb from this link**http://www.dougknox.com/xp/file\_assoc.htm**
after downloading this run this file. always press yess whilie run complet.. i hope ur system will work perfectly as mine...sorry for bad english