I recently bought an all-in-one computer (about 6 months ago) and since then the screen has slowly gone to crap. It was fine the first couple months but over time lines started to appear and eventually (now) I can barely see anything. I have to wait 30 mins for the colors covering my screen to disappear, and even after that I can only be on it for about an hour before they reappear and inhibit me from seeing anything again ( also there are white lines going horizontally across my screen that never go away). So the question is, should I waste money on a USB graphics adapter and connect it to another monitor? I'm hoping that I can just move everything from this current computer desktop and place it on the other monitor and just use this (the messed up screen one) as a kind of "tower"... would that even work?
I do have to agree with rotor123
...is there some reason why you are not looking to get it repair under a warranty? If it was new when you bought it and it is now only 6 months old, then it likely still should be under warranty as most manufactured computers come with a 1 year limited warranty.
Ask to your question, yes, you should be able to use a USB graphics adapter with it. Just keep in mind that USB graphics are not very powerful, so anything graphically intense will likely not work well on the monitor connected to a USB adapter or even at all. I use a USB graphics adapter to add a second external display to my 17" laptop. I can tell you that it will NOT play HD movies through iTunes on that monitor...I have to move the movie's window over to the internal screen or the external monitor connected to the MiniDisplay port that makes use the graphics card in the laptop.
Have you looked to see if you have a video out connection that makes use the internal graphics card...i.e. a VGA, DVI or HDMI port? Most all-in-one computers will have such a port, just as most laptops theses days will. If it does have one, try a monitor hooked to it and see if things are any better.