Fortunately the CPU seems fine.
I got a new cooler for it. That sorted most things out - the 'jerking' was due in part at least to a hot CPU.
However - the problems are still not completely sorted.
I am still getting the Hard Drive stuck sometimes on bootup, and slow performance starting programs. Once they've been loaded once the system runs fine.
I'm suspecting a defective Hard Drive because I'm often getting "One of your disks needs to be checked for consistency" and auto disk checks on startup.
I'm thinking of buying a new hard drive and installing windows on that, and using the second as a slave to transfer the data over and see if that helps.
Is it worth buying a new HD???
Thanks a lot.