Does the keyboard work before Windows starts to load, that is can you press whichever key you need to for the BIOS settings? If the keyboard and mouse are USB powered, try different ports. Can you borrow another keyboard? Have you checked any batteries that might have failed?
When you do find a keyboard that works, tap Function 8 as soon as you power up then select "Disable automatic restart on system failure" so you can see a blue screen with a Stop Error message and post back with the numeric code 0x0000?? and ANY_WORDS_JOINED_UP by underscores. Someone will be able to analyse that and help you further.