it is about 5 in 10 times, when I start my pc it does not boot. and shows a message on screen as follows:
Boot Failure
Insert Boot Diskette in A:
Press any key when ready.

what to do?? I have inserted a bootable startup disk even but nothing happened.
i have also even formatted my pc. i have windows xp installed.
Please help me out. Why does it happen?

i'll be very thankful.