Black screen on startup

Well, my main computer, upon bootup will sit with a black screen on the monitor. Now, the monitor doesnt even detect that the computer is sendign it a signal as it says "no signal input" when i turn the screen on and then remains black.

Normally when i turn my computer on there is a loud whirring noise that thend ies down to a softer noise and then boosts back up to a louder whirring noise again and remains that way through use untill shutdown. Now it doesnt even go past the first stage (it remains with the softer noise). Whats more, the flashing light on the PC case that normally goes crazy upon bott up and game use etc, to indicate hard drive access, doesn't flash once.

All this came after earlier that day i kept recieveing a blue screen of death after the vista loading screen. As a result i pulled out and plugged back in both my graphics cards (leaving them out for about 10 seconds) before reatching the 'crossfire' slide and tryign again, only to find the previously described black screen problem.

I then tried plugging my screen into a different socket (on the graphics card that previously had nothing plugged into it) and i still recieved the same problem with no variation. Upon trying to plug in my old screen (recieved my new one 2 days ago) there again, was no variation.


My system has the following specs:

- intel quad core CPU overclocked to 3.2ghz.
- 2x ATI radeaon HD 4870's om crossfire mode. Overclocked to have a combined graphics memory of 2.8gb's
- 700gb western digital HDD
- 24" benq monitor
- 4gb RAM (4x 1gb)
- 850w PSU
- Vista 64bit Ultimate edition

(sorry i coudltn eb more precise but my dxdiag is on the computer and as noted, its not functioning )



Thanks you in advanced,

~H.