Hi,
I had the same problemb, i think you have the same computer as me, it started when i re-built it, and i cant remember what i did, i am sure that it has nothing to do whith the battery. try cheking that all the wires inside are in firmly, and the CPU is in properly. It that dosent work, try re-building your computer. I think it might be a problemb with the CPU not being in the correct position, or the RAM cards ( maby they are loose?). Chek the hard drive is set as master.