Recently I have noticed that the small red light on the face of our computer stays on after the computer is shut down. 2 days ago the mouse stopped working and then the computer began to crash. On start up it states that the CMOS battery is low. Could this be responsible for the mouse and crashing problems?Replace the CMOS battery.

Is all hardware properly connected? Do you hear any beeps during POST?If your battery dies or is removed, all it means is that your cmos will revert to the DEFAULT settings.
I think your mouse & crashing problems may be something else.I have replaced the CMOS battery and the computer is getting worse. It STILL gives an error message regarding a low CMOS battery and sometimes that the CMOS memory is the wrong type. It only boots up about every 5th attempt now and even in safe mode crashes within either a few seconds or sometimes minutes. The power supply seems to make a bit of a whine and the power switch is fixed to on. The only way to switch it off now is to switch off the plug. The one time it stayed on safe mode for about 20 minutes, it had a continual BEEP every 30 seconds or so.Try TESTING a known working Power Supply Unit on the computer in question.

How old is your mainboard?

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It only boots up about every 5th attempt now and even in safe mode crashes within either a few seconds or sometimes minute