Either an inverter for the screen, or the hard drive has gone bad.
Try rebooting to SAFE MODE by pressing the <F8> key repeatedly about once per second as soon as you press the on switch. Can you hear the hard drive booting up? If you get anything at all on the screen in SAFE MODE, then it may be a problem with the monitor or driver. Otherwise, it is likely a failed memory module or hard drive.
The inverter can be replaced for as little as $15 to $30 and about 18 tiny screws, if you are handy with tools. Same with the hard drive. Your data may be a different issue.
If you have more than one memory module, take out one with plastic or rubber-gloved hands, and try booting with the other. Then reverse the process to try the other memory module. If neither memory module makes a difference, hope that it is only the screen inverter or the hard drive.