Solutions to errors » Photoshop artifacts error! PLEASE HELP!!?

I’ve had photoshop cs4 for about a year now and has never had a problem but now when ever I open something in it it comes out covered in wierd lines :S……pictures..canvases..absolutely everything!!..ive tried re-downloading it but they won’t go away any ideas?? I’ve also tried deleting the settings when I open it but no change …btw heres a screen shot of my photoshop so you can see what I mean: http://s647.photobucket.com/albums/uu199/XXSugarBubblexX/?action=view&current=pserror.jpg

Thanks! and please help!
Just to say that’s it’s definitely not a virus becuase I have norton 2009 and tht found nothing also this did happen once before when I first got it but it went away after for some reason (which I dnt know y)…also I already have pressed the ctrl,alt and shift keys twice before and deleted the setting before but it didnt change anything
thx for the comments so far