Well not freeze exactly. It's a HP DC 5000, desktop. 2.8 Intel processor. XP Pro SP2.
The problem is when it's running the cpu usage is quite high ( 15% - 35% ) average. but it seems to get stuck. The same time after time, the same sound from the HD each time. Accessing Task Manager brings it out of it for a little while, but it sticks again. Could this be because there are bad sectors on the HD.

any help most appreciated.

Yes this could be caused by bad hard drive sectors. Have you tried running a disk check under drive properties

Could your more fully describe what you mean by "...it sticks again..." and "... seems to get stuck..."

If i try running an app the computer just hangs. won't start the app unless i start up taskmanager which seems to bring it around till the app starts. then it just hangs again until i do the same thing again with TM.