I am trying to install Ubuntu alongside Win8 on my laptop, though I can't. For some reason it won't give me the option. I have used a guide I have found here to remove GPT structures with gdisk and I did, and now gdisk only finds MBR structures, but I still won't get the option. I have 3 partitions, and 50gigs of unallocated space. What can be the problem? :S Thanks!
Normally Ubuntu installer doesn't see unallocated space.You have to create ext4 partition from that unallocated space.To do this exit the Ubuntu installer and open up Gparted Utility.
Create a new ext4 partition from that free space.Now run the Ubuntu installer, and it will detects.