You say the computer acts like it starting then doesn't...
Does the fan start running and stay running until you turn off the switch ?
Do you see any leds ( little lites on the case come on )
they usually are near the on / off selector on the front.
**this is perhaps a dumb question , but is the monitor connected to the computer?**
If you don't have a friend with a good working knowledge of puters you should take Detox's advice and take it in to a service shop. Don't ever be afraid of looking like an idiot and asking questions when you dont know something. Asking questions is the best way to learn. The other thing is if you take it in to a shop .....
tell them not to replace anything unless you tell them to , and insist on getting a price before you let them go ahead. You asked if your information will still be on the hard drive .......the answer to that is yes. If your H/D is damaged and that may not be the case ..........information can be recovered by people that specialize in recovering data from defective hard drives.
This is not cheap........but again always ask first.
Remember , you are the customer......they work for you.
hope this is of some help to you.
dl65