Windows no longer starts

Hello,
I can't get Windows to start up on my computer anymore. I was using my computer to watch a DVD the other week and when it popped a notice up that the virtual memory was running critcally low. So I stopped the movie and tried to expand the virtual memory limit. I had a web browser open at the time and the computer closed that automatically. I tried to open it back up and it wouldn't let me. I shut down the computer and restarted it. I stilll couldn't open a web browser. So I tried stopping any unnessessary programs running in the background. After this a window popped out that said my system had to shut down. It had a one minute timer on it. Once it reached the end of the timer, the computer shut down. Now when I try to start it up, I get the safe mode start up option screen. However, it doesn't matter if I try safe mode or not, now Windows won't even start. It tries to and then the screen blinks and I'm back to starting in the bios menu. I've lost the boot CD so I'm not even sure where to go from here. Is it a hardware problem?