Laptop shuts down ! Help !!!!

I have a laptop made by Fujitsu Siemens model AMILO L6825 and terrible headaches because of it. :4-dontkno This is my problem: When i unplug the charger, the laptop is shuting down. The batery level is sometimes 0%, sometimes 100%. I thought the problem is that i have a "dead" batery and i was planning to buy another one, but a friend of mine told me that is possible that the batery to be ok, and another part of the laptop has to be fixed (something about recharghing part).
One more detail, this started to happen suddenly. The batery was ok (it lasted for about 2 hours the day before), but the next day it started to have this BIG problem. So now my laptop is a DESKTOP !!! Please help me, I would really apreciate your answers to this problem. Thanks !