PowerBook G4 reinstallation help!!

I have a PowerBook 15-inch 1.5GHz, I cannot honestly tell you anything more. I don't even know what Mac OS version it was running, or whatever. I lost the installation disc over time and it's come up with a grey screen 😟 Flashing with a folder with a icon in it, and a folder with a question mark in it. (As you can hopefully see from the pictures. Sorry for the awful quality!)

It won't go onto the start up screen, and it basically freezes, so my only option is to hold down the power button to force it off. I've been looking up solutions and trying anything. Some people have been telling me that I need to reinstall the installation discs. But as I mentioned I don't have them anymore. I found disc on Ebay but I'm worried they won't be a match to my PowerBook. I'm so desperate for it to work again. I'm not bothered that I'll lose everything, because anything I had on it wasn't important. I hope someone can please help!

Here is a link to the discs on Ebay: http://www.ebay.co.uk/itm/Powerbook-G4-15-17-OS-10-4-2-Install-Restore-Discs-NEW -/110756429925?_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D2%26po% 3DLVI%26ps%3D63%26clkid%3D6491579106702082365#ht_1118wt_1110