My computer freezes at the boot screen.

This is not really a Windows 8 problem (I think) but I wonder if the experienced gurus here may be able to advise.

I have an Acer laptop which has stuck on the boot screen after a Win 8 update restart.

When it starts the welcome screen launches (the intial Acer screen with the message press 'F2 to change boot device') and that's it. No beeps, clicks or flickering - it's just frozen.

Can anyone suggest what the problem may be?? or where I start looking.

Thanks for any assistance, and apologies if I posted incorrectly.