Desktop Boot and Lockup

Hello, a few days I tried waking up my PC from sleep mode and neither keyboard/mouse worked. I held the power button (yellow light) and shut it off. After turning it on, instead of being a blue light, it turned on with the yellow sleep light. I unplugged the power for a day and turned it back on, and this time it was blue.

Ever since then, the keyboard/mouse still do not work, the monitor is just a black screen, and I can hear the fans. Another thing I noticed is the power button suddenly turns off when I turn the PC on. I have to press it a few times to get the blue light on.

-Can't use the keyboard/mouse therefore can't access any menu.
-Black screen on monitor.
-Power button sometimes shuts off suddenly when turning PC on, needing me to press it a few times.
-Occurred after sleep mode, was not downloading or doing anything.
-Fans are working.
-Unplugged the power cord and checked every cable on the monitor and PC.
-Removed side panel of the desktop and reinserted RAM sticks (3GB RAM altogether) and cleaned out some of the dust.
-Plugged to different power outlets to no avail.
-Used a different, functional keyboard/mouse to no avail.

I hope this isn't a software issue, as I have important data on there. I think it may be a hardware issue, I hope, due to the power button shutting off when I turn it on, but doesn't explain why the mouse/keyboard don't work or doesn't display anything on the monitor. Thanks!