I would use a power supply tester on it to confirm. If that really was the case, none of your fans or hard drives would be able to spin up on only 5 Volts. If you don't have one and neither do any of your friends, you can pick one up one from Frys
here, if you live in the U.S.
If you're in Canada, buy one from
here
And if you're in the UK, you can find one
here.
If you're in another country and can't or don't want to buy from any of the suggested places above, I'm sure local shops have them as well. They aren't too hard to find, and they don't cost very much for a decent, reliable tester.
Regarding the temperatures shown in your screenshot, they look pretty normal, but given the voltage issue you pointed out on the 12V rail... this certainly looks more like a power supply problem now.