I built my father-in-laws PC several years ago. From old spare parts I had leftover.

Specs:
Mobo: Intel D865GLC
Gateway MIDWAY 4000888 socket 478
CPU: Intel P4 3.06ghz 800fsb
Video: Radeon 9200 AGP 8x (128MB) DDR 64-bit, 3DAccelerator
Audo: SIIG DP SoundWave 4 Channel PCI
Ram: 2gig (PC3200 DDR SDRAM)
HDD: 160gig status:healthy, 96gb free space
CD drive: LITE-ON CD-ROM LTN-5291S
DVD drive: LITE-ON DVDRW LH-20A1P [CD-ROM drive]
XP Home edition, SP3

OK, this PC has been running fine since I built it, I did add a better video card last year so he could run some slot-machine games. The only other thing that changed is he had U-Verse installed several months ago, but the PC was running fine until just a couple weeks ago.

He said he was getting an error on bootup and wrote it down:
Reboot and select proper boot device or insert boot media in selected boot device.


So, I agreed to take a look at it.
He brought it over and I hooked it up to my KVM switch and it booted up just fine. (I didn't change anything!!)
I shut it down and rebooted it almost a dozen times, no problems, none. Booted every time.
My wife even shut it down and rebooted it. She asked me how I fixed it and I said I didn't, it wasn't broke to start.

She took it back to him, he hooked it up and it refused to boot AGAIN.

So he brought it back, I hooked it up to my KVM again and it boot just fine. WTH????

IF I understand the error message, it's trying to boot from something else, BUT WHAT??
I'm going to try going to his place and only plugging in the Monitor, Keyboard, and Mouse.
Then see what else he's plugging in, but it doesn't make any sense to me.

Any suggestions?