[ubuntu] Boot from USB issue

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http://ubuntuforums.org – Ok so I have a laptop with no internal HDD so I bought a USB drive, it was cheaper. Now Ubuntu runs great on it, but some times I turn it off and leave it off for a bit I have to go through the whole recovery process. It sees the HDD but doesn't see the Ubuntu files, it says the HDD is corrupted. After I go to use previous version and boot in recovery mode, let it do it's thing and resume normal boot it'll check the HDD, repair it and then boot. Some times it takes a few tries to get it. Now as I said the HDD works fine. Simply restarting the computer does nothing like that, goes straigh (Hardware)