1) Have the brand and model number of the computer. Lots of computers have similar problems but the parts on seemingly similar machines can have greatly different prices.
2) If there was an error message write down or copy the exact error. An exact message means so much more than an approximate description of what something says. For example "No network found" and "No internet found" are similar but theyare symptoms of different problems. The more precise you can be the easier I can help.
3) Do your best to be able to outline what you were doing when the problem occurred. Sometimes the problem isn't your computer but something with a specific program on it. While this isn't always possible, the more detail you have the easier it is to diagnose.
4) Can you repeat the problem? If it is an error message, or something not working right, reboot the computer. Then try to recreate the same problem. If you can't then maybe the reboot was what your computer needed. If you can you may be better prepared to tell me the steps that show the problem.