Round a friends last night and hi pc is like a snail. Turns out he has never run a disc clean up or disc defragment or any sort of 'clean' in 6 years of having the computer. We ran a Disc Defragment and 8 hours later it was still running. Is this ok? Can you just let it run? How long could it take? I am no expert but i keep my own pc up to scratch and clean but bit stuck on this. Thankyou in advance.