using 98se- im getting unexplained crashes usually while using net, system restarts, have done a reformat after a virus and it has happened scince. have none there now as scan done by spybot and McAfee a-v. also gets lot of freezing. defrag and scandisk also run, cant find the problem

Have you done the really long "Thorough" Scandisk process that checks for bad sectors on the hard disk? Bad sectors are physical damage that indicate the start of your hard disk dying and they're an early indicator that you'll need to replace the hard disk before you lose everything. Takes quite a while to run on most systems but you can leave it overnight and it's definitely worth doing.

Have you changed any hardware just before the problem started?