I know this sounds too simple, but have you checked the breaker for the outlets in your office? Have you checked the outlets you've used to make sure that they're supplying 120VAC power?

Next, I would check the AC power cable from the wall to the PC. Again, it sounds like it is too simple, but I've been down this road, and in the past, I found that the outlet (which was off a GFI) was dead due to a failed GFI.

Have you tried to use the case-mounted switch, is that wired up, to cut out the keyboard and USB issues?