My gateway PC is not responding

Hi,
I am having trouble with my touch screen gateway PC. It always turns to a black screen and does not respond. I already checked the ports and plugs and also did some unplugging and then plugged it again to my computer, but it is still not working. I need to know the following:
· What is the cause of this problem?
· How much will it cost if I am to ask for assistance from a service center?
· If I send the PC back to Gateway, how long will it take to fix the problem?
It is also important to note that the time and expense is very significant for me because I will be using my computer for my school work.
