I/O error no such device?

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http://www.linuxforums.org – I though I had Ubuntu installed right. Tried starting up today without cd and got no operating system error. Put Cd back in and tried to reinstall and it keeps going back to the terminal with I/O error no such device. I am totally lost here and any help would sure be appreciated! I can boot up using the CD option to try Ubuntu. Thanks in advance, Brian (HowTos)