I would consider upgrading the OS to OS X 10.4 Tiger for decent performance.
You need a full retail OS disc with a black background with a silver "X" on this disc/s.
You can try and find these on Amazon or eBay. The disc/s maybe expensive.
You're going to need either a full retail OS X install disc or a set of system restore discs.
For the restore discs, You need to contact Apple in order to get OS X 10.4 Tiger from Apple, assuming they still have copies.
Apple Store Customer Service at 1-800-676-2775
These discs will be replacement OS install discs. You will need to give the rep your Mac model and serial number and you'll, also, need a credit card as there is a nominal fee of around $18 for processing and shipping of the disc/s.
The serial number should be on the plate or sticker you found all of the other info.
Assuming the optical drive still works in this Mac, those replacement system restore discs should boot up the Mac.