problem with shuttle SK83G

I have 10 Sk83G shuttle's that are used at a school, 8 of them unexpectedly switch off on their own. and a red light appears on the motherboard.

the units are not very old and have developed this problem one by one.

it uses a FX83 motherboard.

the only way i can get the unit to switch back on is if I unplug it from the mains.... then plug it back in.

any ideas what might be causing this?