We might need alittle more info than that. If you can get your hands on a multimeter, take that and test your a/c adapter to make sure it is putting out the proper amount of voltage. If it is, trying removing your battery and turning on the laptop with just the a/c adapter plugged in to it. Also try a different power outlet to plug into. Let us know more detail on anything else that could have possibly happened before.
Also, if all else fails, how old is the laptop? If it is within one year, I know the manufacturer will cover any failing parts (other than the a/c adapter and battery). You can either contact Acer yourself, or bring the laptop to a major retailer, and with proof of purchase (a receipt) they will send it to the manufacturer for you.
- Daniel