I have an Acer Aspire 3500 notebook.I run Windows XP SP2.It starts fine but freezes up at no certain length of time.It doesn't matter if there are any programs or apps running.I hold the power button until all power is cut to the computer.When I restart,it goes through the disk check to check for errors. Then it boots normally,but soon after freezes up again.NOTHING functions when this happens.If I let it set the fan kicks on and off as normal.What could cause my system to run unstable?I have restored to an earlier time.Nothing! Tried removing programs I recently installed and cleaning out my unused files.Still nothing.Please help.I need my pc for business.