A friend of mine asked me to fix his HP Pavilion Phoenix SE a6755y. When I tried to boot it, it would fail at the HP invent screen and restart. It would do this over and over until it was shut off. I tried to use my own copy of Vista to re-install it but it wouldn't boot from the CD even if I used the boot menu to do it and even got the same result after changing the bios.
My second choice was to use my old Ubuntu 9.04 Live CD to install Linux just so it could boot and stay stable long enough to try the Vista CD again. Which didn't work. When I put the Vista CD in, it just boots straight to Linux even if I try to force it to boot from the CD.
It seems GRUB didn't (or wont) install over HP's default boot menu and even then, I'm not sure if that will help or not. I've tried reinstalling Ubuntu several times with every imaginable setting and tried it straight from the terminal with no results either.
Did the usual message about boot options show up when you first ran the Ubuntu LiveCD or did it just go ahead without any input? Will the Vista DVD boot another computer? It may be that's where the problem lies if the ISO is corrupt or is hiding under a spec of dust on the disk.
The boot options still show up as usual with the Ubuntu CD. It's the HP welcome screen with the normal options. Pressing esc brings up the boot options for using either the hard drive or the DVD drive. Ubtunu Live CD starts with or without choosing this option, where the Vista DVD doesn't start up even when I try to force it to boot from the DVD drive.
It does sound like a flawed DVD - try cleaning it with a fingertip full of toothpaste and wiping that off with a lint cloth and definitely NOT a wood-based kitchen paper. If that fails, can you borrow a Vista DVD? So long as you can see the Product Key on your CoA you an reinstall using a different disk and change the key to your own.
Sorry for the very late reply. My internet has been down.
I managed to fix the problem by enabling boot diagnostics in the BIOS which disabled the HP splash screen and allowed GRUB to load properly. I also swapped the boot priority of the HDD and the DVD drive to boot from the CD and installed Vista successfully.