Thank you for your reply. I hope you do not regret taking this on!
The device is a tablet with blue tooth connected removable key board. I am sorry I miss read my receipt, the number should be P315. It has only one standard USB port, a mini USB which I think is for projection output and a pin hole marked "reset".
I agree that it is the legacy which has affected things althought the original problem of instablity may also be a problem.
I have powered up without a USB stick and it stops - unable to boot, please insert USB drive (or something similar). It fails to move on through the boot order list. I assumed that this was because the windows boot manager, next on the list. could not work in Legacy. I have borrowed a USB connected key board as all mine are PS2 and there is not port on the tablet.
The key is that I do need to disable Legacy but how?
The reset button didn't change anything. It still says no bootable device.
How can I tell what version of USB my keyboard is? The only information, apart from Made in China, is the date sticker 2009.
OK this is getting too difficult.
In summary it seems that when the computer says press F2 to enter set up I need a USB 1 keyboard which should cause the computer to repond and allow legacy to be returned to UFEI and then I will be back with the original instability issue.
I think I will have to take the computer to a repairer.