Did you uninstall any previous Antivirus program before installing the new one?
Did you get any error message when the programs crashed?
See if you can find the cause of the error.
Click Start, Run, type eventvwr.msc and press Enter.
Look at the System Log and Application Log and double click the error entries, to see if the information makes any sense. If there seems to be a common cause, then that's the one to troubleshoot.
Or try uninstalling your antivirus (don't connect to the net without it) and see if the problem disappears.
Or try using one module of memory at a time (if you use more than one) to see if memory may be the cause.