hmm, with your specs can you try to
- go into manual partitioning, then select and delete each existing partition,
- when there is only empty disk-space left set up a new
a) swap-partition (2GB)
b) ext4-partition (50GB) and mount it under "/",
c) ext4-partition (remaining disk space) and mount it under "/home"
then continue with the installation, should work.
good luck,
-p.