Ubuntu :: Unable Boot After A Recent Update

I've been running ubuntu on multiple computers for about 8 months now, installed on one computer as it's only OS (XP ran too slowly), and as a side OS for two others, one running XP and one running 7.The problem is, Ubuntu recently stopped booting on my Windows 7 computer. The option shows at start-up, but when I select it, the computer restarts back to the boot menu. I had recently installed an update from Update Manager that required a Restart, so when I restarted it to finish installing I left it to have dinner and it restarted into windows.About a day later, I wanted to boot ubuntu again, but my computer simply restarted, and has been doing this since (it's been about 3 days). I'm not sure if this has anything to do with it, but the last thing I installed before the update was a 1st person shooter game, I can't remember the name, but the icon was a "ka" symbol in katakana.