I using an AMD Athlon XP 1800+, 256mb DDR RAM, 4MB S3 Video Card running Windows XP.
Sometimes when I start up my computer it doesn't start, I just get a blank screen and the monitor light flashes orange.
Can someone please help me with this problem.

Thanks

Sounds like a loose connection where the monitor is not detecting the computer is on.

Try to reset your BIOS,it will surely help yeah... as long as I remember in AMD Athlon there will be a switch,small one... move its position and start your computer. Your BIOS will be refresh and computer will run