[TZids16I]

I'm having a serious problem here with my computer. It's been going on for almost a week. I'm having a problem with booting up my computer. I get the message on the black screen of a Disk Boot Failure. It worked fine yesterday, but I don't know what I did so that it worked. The computer is an EMachine and is about three and a half years old. When I go into the boot menu it shows that the Hard Drive is listed first, which isn't something that I set myself. When I select the CD/DVD drive to boot first, I press the Enter key, but it doesn't work, because it always returns to Hard Drive as being the first thing to boot. Is THIS the problem? The day before, Sunday, I found a disk with Unbuntu on it and was able to use it to access the internet to some degree like I am now. It's not installed, it's just a live disk. That's the only reason I'm able to be here today.