I recently had to change MOBO and processor on a computer, seems to be running fine but System Guard says my 12V is actually 15V.

Since I had been running AMD stuff for some time, and now changed to intel, I thought this may be a problem with the PSU, so I got another P4 approved one. Exactly the same problem!

Seems to be running fine, I wouldn't have known unless I checked with the software (no reading on bios) been going a few days and perfectly stable at any load, could this be a problem with the monitoring system or should I worry about it?

Have a 300W PSU with Celeron 1.7 and a Fujitsu-Siemens D1527 MOBO. Only PCI thing is a modem.

Any help greatly appreciated

It's probably the motherboard measuring it incorrectly if it happens with two different power supplies. I'd get an el cheapo multimeter from Radio Shack and check it with that.

I never trust software monitors for accuracy. Truth is, most of them are not very reliable. Check it with a multimeter as Tarkus suggested. If you are actually getting 15v on the 12v rail, that could cause some serious problems. I doubt that is the case though since two PSUs are getting the same reading. It is most likely either a faulty sensor or the software. I'd say it is probably the software.

Thanks, fairly reassuring. I'll try and check it with a multimeter to make sure though.