Adding gpu to prebuilt



Depends on:

Can your psu handle it
Does the x16 slot have some weird limit
Does it actually fit inside the computer
Is there enough airflow in the case to not make it overheat

Listing your prebuilt will help a lot.
 
When you decide on a new video card, go to the company web site and look at what power supply wattage they suggest. Note that they expect people to go "cheap" and get a poor quality PSU. You can actually run a very good power supply that is lower wattage than they suggest. To those not in the know, the question seems either unimportant or lack of knowledge can keep a person in the dark. That is often the reason hardware is sent back. Very often the problem is not with the video card but with the power supply. Make sure you purchase quality. You can search for outstanding reviews here: www.jonnyguru.com

measure from the back of the case [over the slot where the video card will be] to the first obstacle inside the front of the case. Measure from the PCIe slot to the outer edge of the case, and if necessary measure how thick a card will fit, as many newer video card companies use thicker coolers on their cards.

As to the question of air flow inside the case leave a question here about that issue.

Please leave a link to the prebuilt computer you have.