Linux partition shows up as unallocated

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http://askubuntu.com – I had Windows 8 installed with 2 Ubuntu parititions in dual boot, everything running well. I hated Win 8 so I installed Win 7 over it by deleting my 80gb Windows partition and installing it in there. But now I can't boot Ubuntu up, since obviously Windows has overwritten Grub. Routine stuff, so I booted into a live CD, opened up GParted, and I see that the 80gb space that is supposed to be two 40gb Ubuntu partition is showing up as Unallocated! What's happened here? Is there a possiblity that there's some error in detecting the partition? I'm 100% sure I didn't delete that partition in the W (HowTos)