Black screen, Won't Boot

Okay, so I've had my Dell Inspiron 1720 laptop for about 2 years. I've had my problems with it but they always work out.
The Black screen.
This has been going on for about 4-5 months. I can use my computer, granted its been off for quite some time, then the screen will go black. The computer will still be running and all the lights are on. to get it to fully to turn off i have to...
1. hold down the power button for a good 5 minutes
2. Unplug the power cord
Or 3. Take out the battery
I'll let it sit for a few minutes then try it again. Most of the time nothing will happen. sometimes, it will load fully but the screen will shut down minutes later or it will get though some of the boot up and then the screen will go black. When this happens sometime i can hear the boot up noise (when i windows logo is displayed) if i put in my password it'll make the log on noise...
This has happened to me before when i still had my dell warranty and they just told me it could be that the battery and the power cord was doing something, I don't know. But what ever they told me worked.
Okay, so I've tried down loading Windows updates i've missed because they messed my computer up, I've tried pressing F12 to run system checks, all were fine, I've tried hooking up my computer to another screen to see if that's the problem, I've tried Ctrl+Alt+Del, Nothing.
One last thing, my computer it pretty much like Frankenstein's Monster, meaning it has almost none of the original parts. Almost all of them have had to be replaced because I'm either a moron, or Vista just decided it was gonna burn out my hard drive.
I'm just completely lost about what to do so any help would be greatly appreciated!!