Mark,
Before you go into full panic mode I have something for you to try. My computer on occasion will do basically the same thing, I hit the power button and Windows will not start and instead I get a message basically referring to some link that is missing, or something to that effect. This started happening with increasing frequency a few years ago, in fact just about every other time I turned it on, and it dawned on me that the weather had changed from more humid to much dryer because it was late in the year (I have had similar issues with other connections in the past due to humidity levels changing dramatically). What I did was.... with the computer OFF and unplugged, find the cable that goes from the hard drive that plugs into the motherboard, disconnect it and re-connect it. In my case, after doing this the problem went away completely and I attributed it to just a connection that wasn't passing a signal. If it does it again with frequency I now know what to do. Worth a try anyways. My experience with hard drives that have acted up in the past is you should be able to at least get it to boot and get Windows up and running, it may take several attempts, then once it does boot you can do a 'disc check' to see if you have bad sectors or what's going on.
Marc