No idea. I always thought custom built computers were full proof but I guess I was wrong. Anyway, is there anything I can do besides cleaning the fan?
I think we're confusing what you mean by "custom built."
Typically, when telling a computer geek you have a "custom built" computer, that usually means that all the parts were bought separately (case, motherboard, processor, memory, power supply, video card, hard drives, DVD burner, etc.), and put together without the blessing of a brand name like Dell, HP, Gateway, or whatnot.
In this case, you have a "factory built" or "brand name" PC. Perhaps Dell had an option on its website for you to "customize" it or select your own parts, but using the term "custom built" to describe anything with a brand name on it is going to cause confusion.
Onto the problem at hand, overheating could be the problem. You can either clean out the fan using canned air (the stuff that you get from an electronics store that they don't sell to minors for fear of them trying to get high off of it), an air compressor, or a vacuum. Just be careful with whatever you use.
Alternatively, it could just be a bad video card. Usually when there are artifacts like that on the screen, that means the card is bad regardless of what temperature it's running at...
