sheer exasperation

I cannot even begin to count how many times I've run Vista Startup Repair. Many times it's heart-stopping since I can never be sure that the computer will actually boot up. It's amazing to me that Vista boot up can be so easily corrupted. I don't know what corrupted it (very possibly my ISP software). The other night I had Vista make me a backup, since I don't know when I'll just not be able to boot at all. Last night I re-installed Vista as "upgrade" since the other option, clean install, will wipe out the drive. When it finished, it had the audacity to tell me that my copy of Vista is not genuine and wouldn't let me into my computer until I do something about it. One of the options is to activate Vista online, but it wouldn't let me login. Instead, it had the option to set up a connection. I had to dig and find an access phone number for the ISP. Amazingly enough it connected, even though my ISP requires the ISP software. After logging in I dug around the internet to no avail about the authenticity thing, then rebooted and Vista seems to have corrected itself. The computer seemed to be working again. Except today I come home, boot up and it tells me I don't have a bootable device. A press of the key to reboot brings up the computer okay. The last resort is to do a clean install, i.e. wipe out the drive and start from scratch.