Morning Connor
depends on if the CD/DVD you've left in your computer
1. is bootable or
2. if there are other information which tried to get loaded (f.e. device driver)
3. has scratches on the surface
For 1.
Usually the media should boot. If it doesn't you should check the media (s. 3.) or if other media are working wi´th your optical drive
For 2.
The OS has noticed "bootable" information (sys, inf files) but can't load em up. It'll try it again and again til it stucks
For 3.
You should be a bit carefully with ya media mate

;)
Greetz
BU