Manual for compaq c700

Most likely the main board...try locating one on Ebay, then go to you tube for a "how to replace" video.

If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
Line faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent. Faults to all LCD & Plasma screen are similar, irrespective of its brand and screen size.

The LCD screen is faulty and will need to be replaced, go to www.ebay.com Type: make and model refine search to screen, first! hook a spare monitor to the video output usually on the back, if picture okay! the above mentioned needs to be changed, but! if both show the same symptom it is the video graphics card that is part of the motherboard.

bad LCD.
costly fix
or bad GPU chip local. to LCD , but I think not.

If your screen is filled with hundreds of vertical or horizontal lines, your screen is cracked.

Seems like an issue with the display.
To confirm it take the system in safemode and check also take the system to BIOS even in BIOS the same line is there then the issuue colud be either with the display or with the motherboard.
To confirm it try connecting an external display and switch the display to the external monitor and if still the line is comming in the external display then the issue is with the motherboard else the issue is with the LCD

STK392-560 STKS convergence CHIPs Replace both of them.

Send me a Digi-pic of the screen please.. Good starting point..
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Does it only show up on Cable or does it shows on all Dvd, Cable, Sat, etc ?

Open up the TV and unplug and re-plug the connectors to the circuit boards. This is most often caused by a poor connection of the circuit board connectors.