My imac is stuck at the loading screen and wont start up...

What do you see on the display? What do you mean by the 'loading screen'?

Does the system startup successfully in Safe Mode? You can do this by holding down the shift key as soon as your hear the startup tone after powering on the system. For more information see:

http://support.apple.com/kb/HT1455

If the system boots in Safe Mode then you most likely have a software issue. Depending on the OS version you are running you can resintall the OS which may resolve the issue.

Me too... What do I do now...?

Since you purchased your iMac long before the Lion OS was released your system should have come with a set of DVD's that can be used to reinstall the OS and applications. If you can locate those disks then stick the Install DVD into the optical drive, then power on the system while holding down the option key. Your system should boot with a menu showing the bootable volumes. After a few seconds you should hear the optical drive whirr and then see the Install DVD appear in the menu. Select the Install DVD and boot the system. Once booted you will have to select your language. Normally this disk is used to reinstall the OS, however for this exercise I would like you to pull down the Utilities menu in the menu bar and select Disk Utility. You can use the Disk Utility to check whether your hard drive is OK. If it fails the SMART (Self Monitoring Analysis, and Reporting Technology) status then you will need to replace the hard drive. You should also run the 'Verify Disk' and 'Repair Permissions' options if the SMART status indicates the drive is passing.