HP monitor / computer emergency / issues help

Hello, my HP Pavillion Meda Center m8330f Desktop PC will not turn on. It seems to be turing on but the monitor is not responding and when turned on and then off again the screen says no signal and then monitor is going to sleep. This happens every time, unless the monitor has no response at all. Before this problem occured my computer had to be turned on and off several times before actually starting. Sometimes it even need to be startup repaired and/or restored. When I finally got it to turn on it worked for about five hours straight and when I tried to switch user accounts the monitor went to sleep and I restarted the computer as usual. From there the computer began a disc check. When that was complete it needed to be restarted again, and hasn't turn on (computer and monitor) sicne. HELP. HELP. HELP. HELP.