Need help, brothers computer

My younger brother has a windows 7 desktop computer, 32bit.

So, here is the problem. After we hit the power button, the computer makes its loud whirring sound as usual (I assume the hard drive). After 5 seconds exactly, the monitor goes black and we can't press anything or click anything. Its not the monitor, we have tried new monitors and replugging them in. Also, once the monitor goes black the computer stops making a noise. Our father assumes the hard drive is dead. Any help? We really don't want to have to reinstall windows 7.

Thanks in advance