Imac g3 error 10 & illegal instruction

have had an imac g3 for several years and was too busy with windows to use it now that i have used it it seems to have died, as son as i start it up and it loads the mac os starting up windows a box with a bomb appears and says sorry......etc. error 10 restart while holding the shift key, so i do. then i get a new error "illegal instruction" please restart while holding the shift key, so i do and i get he same screen over and over. how do i get my mac back it was fun while it lasted but if this is how macs are I'm just going to have to switch back to windows. please anyone who can help it would be appreciated.

You will need your system disks. Insert the installation disk and hold down the C key while restarting your computer.

After your computer starts up, click on Disk Utility from the Installer menu, and choose Repair.