Just reinstalled a PC for my neighbour as it was running incredibly slow.
It's not the best computer in the world as she only uses it for Facebook!

It's a Pentium Celeron with 768Mb RAM.
It's fine for the first few minutes, then it almost locks up.

I managed to load Task Manager (which took 15 minutes to load) and it has the process 'System' using 99% on the CPU. I've looked about it and some are saying to update the machine, some say it's anti-virus related.

Running Avast Free/Malwarebytes and XP Pro with SP3 - and almost all updates are done.

Anyone got any ideas?