Help pressed power button and nothing happens

So a few months ago I had major issues with the drivers on my computer starting with the drivers for the cd player and essentially could not figure out a way to fix it so I turned the comp off and set it aside for a few months and decided that since it didnt have anything critical and I needed to upgrade the HD anyway I would just buy a 500gb hd and just start out fresh.

Well after a few months of not touching the computer and it sitting unplugged I took it out and put in the new hd and removed one of the cd players and hooked everything back up and now when I press the power button nothing happens. I see the green light on the mobo but nothing happens when I press the power button. I flip the switch on the back and press power button and the fans will jerk but wont spin. I disconnect the new hd and press power and nothing happens. I have no idea what could be wrong with the comp other then maybe somehow the PSU has gone bad or the mobo/CPU is bad but Im hoping its something else as Im pretty much the stereotypical broke college student with this being my only computer and dont have the $$ to get new hardware should anything break. Any ideas on whats going on?

Thanks, for the help. Another forum suggested that I leave the comp powered for 24 hours as the CMOS battery might have lost their charge in the months that my comp has been turned off. Another possibility is that one of my USB ports are shorting out since I have for the past year had one that was picky and didnt always work, gotta check these out when I get back home but any other ideas are welcome.