iMac 5 turning on but not starting up fully

Those large negative error codes for Internet Recovery Mode are due to some networking issue. Unfortunately Apple doesn't provide any explanation for most of those error codes. Best thing is to connect the iMac directly to your router for a faster connection which bypasses difficult to troubleshoot WiFi issues.

You can also try power cycling the router and waiting at least five minutes for the router to finish booting before you try Internet Recovery Mode.

Please click If your Mac doesn't start up all the way - Apple Support for the troubleshooting steps. If you continue to have problems then take the computer to your local Apple Authorized Service Provider to have it serviced.

Also, we cannot help very well if we have no idea which iMac you have. iMacs have been made for over 20 years in hundreds of configurations, many many versions of Mac OS etc. So we cannot guess what you have. Please look over Writing an effective Apple Support Commun… - Apple Community to get a good idea of what we need from you in order to help more.