i have had this problem for the last 4 days, as soon as i turn my pc on all i see is a mixture of red, green, blue and white lines/blocks going accross my screen . I am pretty sure it isnt the screen because i tried the computer in another screen and the same thing happens. . i think someone might have pulled out the plug the day this happened however i am not sure so dont take that too seriously. here are 2 screenshots of what it looks like wen booting. The pattern changes as it goes through different stages of booting and sometimes it ends up just being black sometimes it doesnt. i would apreciate it very much if you could tell me what you think the problem is and how it can be solved.
lines.JPG
blocks.JPG

Hi there and welcome to PC Help Forum

I'm going to state the obvious x 2

1) I think it's your graphics card (open the case and check the fan is still spinning on the graphics card)
2) Take the monitor to a working PC or laptop and just make sure that it works ok..I am sure it will.

Thanks for the reply
the graphics card fan is still working
and the monitor does work with other computers

Then I'm afraid it looks as though your graphics card is probably dying. One last test would be to put the card into another PC...just to see if it displays the same rubbish upon boot.