Sorry to hear that. Sometimes it just happens. Did they describe the actual fault?

All sounds a bit dodgy, Mobos either work or don't and I've have fixed over a dozen boards with strange behavior just like yours, the fact you got it working sometimes I wouldn't give up.

There are other ways around and this could indicates the bios may need reloading or reset Bios to defaults. What is the exact model of the motherboard - printed on the board.