Ubuntu 10.10 has been running great, but now since I did the updates it randomly slows down or stops responding

Ubuntu 10.10 has been running great, but now since I installed the updates it randomly becomes very slow to respond, or sometimes quits responding all together. In one instance I brought up the system monitor and it showed the swap memory at 100 percent and the cpu was very low. There was no applications running at the time. Another time, I brought up the system monitor, and it showed the cpu as running very high and the swap at 0 percent-also with no applications opened. Then one time I could not even bring up the system monitor at all and could not do anything else either so I had to do a hard boot. In all cases, rebooting the machine restored the system to operating as normal, but it keeps reverting back to this condition for no reason at all. What can be done to eliminate this problem?