Q: Tried resetting my iMac, now all i get at boot up is a flashing question mark?

The folder with the question mark means the computer did not find a valid disk to boot from--this is because the hard drive was erased.  You need to re-install the operating system.  Depending on how old the computer is, this can be done through recovery mode or using the original installation disc.  If the computer shipped with Snow Leopard or earlier then it may not have internet recovery.  Some computers that shipped with Snow Leopard can be upgraded to internet recovery.

What year is your iMac?  If unsure enter the serial number at https://checkcoverage.apple.com

Computers that can be upgraded to use OS X Internet Recovery - Apple Support

That computer will not have internet recovery.  It also most likely did not have a recovery partition, the recovery partition's were only added with OS X Lion and later.  If the computer did have a recovery partition but the disc was erased instead of just the startup volume, then the recovery partition was also erased.  If the computer had Snow Leopard or earlier you will need the original installation discs.  If you do not have those discs then a Snow Leopard disc can be purchased from the Apple Online Store.

Put the disc in then restart and hold down the C key.

https://support.apple.com/en-us/HT201255