[Neil]

Sounds to me like you just had a software problem. Your Dell probably came with a restore disk to make it look like when it was new. That will more than likely solve all your software problems but you will loose anything you don't back up. The noise I would guess is only a fan that needs replacing or usually you can re-lubricate them. They are cheap so sometimes its best to just put a new one in. Deffinately no reason to buy a new PC if the old one was a good enough spec for what you used if for.