"lock-up" can occur while on the web or email. Control-Alt-Del will not work, nor will normal shut-down process. Must shut down the computer from the on/off button and then restart. The problem seems to have started after I installed a SpySweeper update. Any ideas?

My suggestion is to get rid of the Spysweeper program off your machine and get a different one instead as this is obviously causing you the problems. I tried this program a long time ago and didn't like it as it did the same thing to my computer which meant a lot of spyware got lodged onto your machine. The spyware is what is locking up your machine. I use Ad-Aware which is free.