12.04 boot failure after update

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http://askubuntu.com – I am using 12.04 and updated using Synaptic Package Manager. Now, however, when I turn on the machine it fails to boot, just a blank screen. If I shut off the machine and start it again and press F12 (on my laptop) to get the boot menu and select the default for HD-0 it boots OK. I had previously used Update Center and had a similar problem, which I corrected by reverting to "Previous" setup. Are there any fixes for this problem or am I unique in this situation. Ubuntu 12.04 Lenovo G575 laptop msanderz Thanks in advance. (HowTos)