MB's are quite reasonable on eBay, but I also understand that can depend on where you are. Might be time for a good deal on a newer refurb if you can find one where you are.
At some point while using my Dell 390 my keyboard and mouse stopped working I've tried clearing the cmos, re seating the ram and CPU. I've tried removing my ssd I'm not sure what to do it's like the USB isnt sending power to the keyboard I've also tried different keyboards and mice I'm really not sure what to do it dosent even work in bios it just automatically puts me to the windows boot screen 
Keyboard and mouse not working