I thought it might be a failing drive so I've just finished checking the drive... but Seagate utilities shows up nothing wrong on the drive.
Tried turning USB legacy on/off with no change.
The system was working properly immediately before plugging in the WD drive... and ever since has been playing up.
The boot problem occurs even when the drive is not connected. The machine only locks up when the drive is connected... and usually after copying some files... not straight away.
It sounds a bit like the problems in this thread... but not exactly the same. Should I start a new thread?
When it plays up you can't check to see which process is creating the problem as no new processes can be launched and you can't shut down anything either (mouse is still moving so not a total lock-up).
After booting it runs fine... so other than the long wait to boot there's nothing else wrong with it.
The machine is an AMD x6 Phenom with 4GB memory. 32 Bit Win7, 1TB boot drive (Seagate), 1.5TB WD drive (for storage). Asrock motherboard with SATA3, USB3, onboard graphics and DDR3 memory. Everything is pretty new and the whole thing runs off a UPS to protect it from power fluctuations.
Anyone got some ideas?