Computer starts then black screen sometimes why????

Sony Vaio desktop that is about 4 years old.
Starts great most of the time I get 1 beep also.
Then once in a while I go to start it,I get no beeps,computer sounds like it is starting,fans spinning not sure if hard drive is spinning and I get black screen.
Also sometimes I have experienced desktop is broken up like little squares on screen view broken up,is that a bad video card and causing the failing bootup?
If it is video card causing no boot can I install a new one on motherboard to fix failing boot.
Bad power supply?
Bad motherboard?
Bad hard drive?
Bad CPU?
Should I try clearing CMOS?
Should I try a new power supply.
Is there anyway to test power supply while boot is failing?
Please help....

Im not understanding your actual question here...

What is the exact issue you are having with this computer??

Is it that you have a black screen upon boot up?

Or the graphics are distorted?
If it is causing a issue upon boot up it is too early to tell but your graphics card might be going bad, because I read something about you having a black screen and or view that is "broken up". I would try cleaning the computer from the inside with compressed air and use it a while see what that does...

Is this a desktop or a laptop?

Edited by JUICYboy, 13 January 2011 - 11:16 PM.

Sometimes nothing on screen,I can hear computer starting and it is a desktop.

I would try uninstalling the video drivers...then reinstalling them.

Louis

Whats the model number of this Sony system?

Sony Vaio desktop model# VGC-RB50