I'm thinking that this issue has nothing to do with you changing your CMOS battery.

We might want to bring to life again the chance that this is your power supply. Disconnect power from the parts you don't need. Make sure the computer is off, and then disconnect the power connectors to your CD-ROM drives, and extra Hard Drives. Just keep power connected to your Hard Drive that has your OS Loader and Operating System on it. Also, if you have onboard video, take the other video card out and use your computer's "onboard" video card. This should reduce the amount of power your computer's parts consume during boot-up (because they are disconnected and don't boot up) so you might be able to get your computer started.

DO NOT PLUG STUFF IN TO YOUR COMPUTER AFTER IT IS ON! You must remember to power off your computer before plugging hard drives back in, etc. Just a warning. If you can get it started with nothing connected, you may need to look at buying a new power supply, because it could be that your current one has reached the end of its days. A weak power supply can make a computer reset itself when you are booting it up. It can show problems at other times, but in our case booting up is the biggest factor.

If it doesn't work, either your power supply is too dead to power up with very few things, or the problem could be something else... And this has nothing to do with the CMOS battery, BTW...purely concidental...