My windows xp has been working OK , bur a couple of weeks back , I am unable to cut / paste /copy , also the mouse does not scroll some times ,

Can you not cut\copy\paste in just a particulare program or where are you trying to do this function at?

Do you have a laser mouse or a mouse with a ball in the bottom of it?

It's sound like your mouse my be dying. :eek:

Until it's fully dead, remember these shortcuts:
COPY = Ctrl+C
PASTE = Ctrl+V
CUT = Ctrl+X

Ctrl is on the lower left hand side of your keyboard. You will press that AND the corresponding letter.

Well, more info needed buddy. Still I guess you are running out of memory. Copy/cut needs text to be copied to clipboard and also involves chain of process. If you run out of memory, you may face such problem.
Try increasing your page memory and free your c drive with min 200mb of space for xp.
Well, I don't think there is something wrong with your mouse if its having ball. To check, remove and try using it on other computer.

Nyways, does this happens as soon as computer is started?