Imac G4 slow after fitting new battery

I bought a G4 700mhz last week from ebay. When I turned it on I was surprised how fast it was but the clock and date was wrong , so I've installed a new battery today .
I turned it on and it was fast as usual and I set the correct time and date then I turned it off then restarted after 5 minutes but it took ages to get to the desktop screen but finally the time and date are correct.

Also the iDVD pop up comes on all the time and the DVD tray is erratic.

Please help.

Thanks

I did what you said, restarted and put the date and time in, I then for some strange reason clicked on PhotoShop and it froze the imac.
Now when I turn on I get the finder and question mark box flashing up. I've had to order some installation discs to see if that will work.
I have bought a faulty imac !!

Thanks