Acer Aspire one Netbook won't boot up.

Hello,

I received my Acer Netbook in September of 2009. It has worked perfectly until a few days ago. When I turn it on, it shows the Acer logo and then goes to a black screen with a flashing underscore in the upper left hand corner. If I try to access safe mode, or press any keys at all, it makes a shrill beeping noise, and does nothing else. The only thing I have been able to do is press F2 and go to the startup menu. I tried loading the default settings like the help page suggested, but it didn't work. Please help!

-Mack