Like purple lines? red lines? Green lines? Black lines?
I didn't bring my crystal Ball to work today so I don't be able to get all the details from your mind and fix your issue, so you may have to give us a little more detail.
Lines on a screen usually indicate a pending graphics card failure. I have seen this a few times with different graphics cards on allot of different machines. What is your machine model number and what GPU do you have installed?