I wanted to leave you with some advice on a common computer mishap, should you encounter it. I see this one a lot. When your computer sounds like it is starting up but you get no longer on the screen, it may not be a serious issue.
If you hear a lot of beeps — then it probably is quite serious. This means that the motherboard (Mac: logic board) or hard drive is probably dead. You will have to make a warranty claim, consider replacement, or contemplate a significant repair.
However, there are other cases when your computer sounds just like it always does but there is simply no video output. You may even see some picture but it may only be a mouse or an inverted screen. In those scenario, the cause is going to be either the video card or the monitor. I totally understand that with most laptop, or an all in one device (iMac) the screen is built into the computer.
The quickest way to troubleshoot this is to plug in an external monitor into your computer. If everything starts up normally, you know that the problem is your screen / monitor. You can certainly use the other monitor you plugged in until an appropriate repair / decision is made.
Unless you are a 2 desktop household (with free standing monitors), I think the following would make up a perfect Computer Emergency Kit if you have serious computer users in your house
1. An inexpensive monitor with the appropriate cord / adapter for your computer. You can get a decent monitor for well under $150 (19 to 23 inch) at Amazon, NewEgg.com, Staples, or Best Buy
2. A wired (not wireless) mouse and keyboard. You can get a basic mouse / keyboard set, ie. Logitech brand or similar, from one of the aforementioned stores for $30 to $40