Here what i would do:
1) backup the documents you can still access if you haven't yet
2) try to recover access to Windows this way: https://help.ubuntu.com/community/Re...ta/7Bootloader . If it fails, reinstall Windows.
3) reduce Windows partition to 50GB via WIndows partitionning tools.
4) install Ubuntu the standard way (no Wubi!): https://help.ubuntu.com/community/GraphicalInstall

if any problem, please indicate the URL provided by Boot-Repair