Calm down and think the situation through.  More than likely, your machine is not destroyed.  Don't assume that you need to throw your computer away and buy a new one.  Think about what isn't working and what is working.  Write down error messages and any quirks you've been noticing.  This way, if you have to call for help, you can tell them that your machine reported a failure of a particular system file and an answer can be found.  Without this information, the conversation will become like this:

User:  My computer's broke.
Technician:  What do you mean?  What's it doing?
User:  Uh...I can't get on the internet.
Technician:  Okay, I need you to click on the start menu...
User:  I can't.
Technician:  Is the arrow not moving on the screen?
User:  No, the computer won't turn on.  Why can't I get on the internet?

This was a real call.  What was wrong with the machine?  The power supply had failed and the computer wouldn't turn on at all, so the internet wasn't a real feasibility at that point.  Calm down and think things through.

Update and run your antivirus and spyware removal tools.  Much of what goes wrong with a computer can be fixed by removing one piece of spyware or another.  Some spyware put nice little smiley faces in emails and such for you, but may open the door for things that block wireless access or network access.  If you can't get updates, run a scan anyway.  If the date of your definitions for the scan is too old, that's one thing, but if they're only a week old and you can get the scan to work, you might get something.  The same is true with viruses.  Also, if you cannot connect to the internet from your machine, you can try at someone else's and bring the file over on a CD or a JumpDrive.

Take notes.  One of the biggest problems any technician can run into is going in blind.  The above conversation was an example.  The technician could have just had the user in question bring in the machine and would have been focusing on the internet problem only based on what's going on.  Now, this being said, we don't expect perfect notes on what is going on with your machine, but things like error messages, viruses found on your machine by scans, strange windows opening up without your input, any of that information can be helpful.  Even if you don't know the name for what you are seeing, write it down and describe it.  Chances are, the technician might be able to figure it out based on what you describe.  This can cut down repair time as the technician can focus more on one thing than spending an hour trying to find the problem from "it's broken".