If you bought a retail or system builder version of W8, you should be able to put the Windows disc in like you are going to install the OS, but there will be an option to "Repair my system" ( or something similar to that ). Try that first, otherwise you may have to re-install.
If you have an SSD and you are going to try installing again, you might want to try deleting the volume ( un-formatting ) first on another computer ( in an external drive ) and then re-install it and let the Windows 8 disk format and install the boot partition and the OS all in one step. Normally it is not necessary to have an un-formatted drive, but it seems some SSD's work better when the Windows install disc does all of the operations for you.