how to fix

[debbieann]

how to fix this program has performed an illegal operation

[PvtSniper]

usually reinstalling should solve the problem, unless something else is crashing the program

[simsfreq]

Press Ctrl-Alt-Del and see which programs you are running, (on the Processes tab) do a quick google search on the exact name of the process (with the .exe if it has one) and see if it could be a virus or just an annoying program which starts itself accidentally.
Put the processes in alphabetical order to make it easier to keep track of what you've already checked. If you want to end the process click the "End Process" button in the bottom right. If you're in any doubt don't end the process. And NEVER end the one called "Explorer", this is what keeps Windows running! The only others I can remember is "alg.exe" which enables all local connections (network connections, internet connections) and "spoolsv.exe" which is the thing that makes your printer and/or scanner work.
Don't worry, if you do accidentally end the wrong process, restarting your computer will start them all up again. If you find a large number of viruses it might be a good idea to invest in some antivirs software!