Hi, after it stopped responding, I went for coffee - about an hour.
It's a relatively new PC. ASUS Maximus formula, 750G SATA partitioned to C: D: & Ubuntu.
I was trying to replace Ubuntu w Fedora. Tried first with DVD, but it asked for Fedora Disk 1 partway through, so I downloaded, checked sha1sum, & reinstalled from CDs.
Don't know what else counts as "relevant"...
BTW, there may be BIOS issues - I reset BIOS to default & was able to get to GRUB. Now when I pick OTHER, Vista boots OK, but when I pick Fedora, I get a blank screen.