ubuntu is crashed while booting up

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http://askubuntu.com – I'm dual booting W7 and Ubuntu (installed from Wubi). I've had it up and running a few times but today ,i have pressed power button multiple times while booting up and I'm getting a message from Windows Boot Manager when I select Ubuntu that wubildr.mbr is missing or corrupt. Any help would be greatly appreciated. i have installed on G drive and the .mbr file got corrupted.I thought of uninstalling it.But now G drive itself is is not opening.Lots of other data is also in G drive.Kindly help me in fixing this issue.am getting the below error when trying to open G drive. G drive is not access (HowTos)