I don't know whether you have solved your problem yet with the previous answer, however I run 3 home built PCs, one runs Windows 7 which I don't have any problems with and use as my main machine for the last 2-3 years, an older machine triple boots into either Windows Me (for older games only and disconnected from internet), Windows XP (for older programmes that are incompatible with either Windows 7 or 8) and Ubuntu 12.04 via Ubuntu's GRUB menu.
I made up my latest machine – an AMD six core – in December 2011 and had great trouble installing Windows 7 which I put down to bad motherboard SATA drivers, I had no trouble installing an earlier version of Ubuntu and did eventually manage to install Windows 7 on a second disc (on port 1 – Ubuntu being on port 0), however after installation I kept getting disk errors on choosing 7 from GRUB and on the occasions it did boot it would occasionally freeze.
I left matters in abeyance for many months as I wasn't relying on this Windows insatallation until last week when it did boot into Windows 7 and I managed to upgrade it to Windows 8 without any problems until again I got disk errors when I either booted into it via GRUB or by using the motherboard boot option.
However this time it told me that there was a BCD file problem – a message I hadn't seen before. Booting into Linux and examining the Windows 8 system reserved partition, I then found an earlier version of the windows BCD file in the Windows 7 backup file under
Windows/Panther directory, so I suggest that you use a Linux Ubuntu disk that you can boot from and examine your Windows partitions and replace your BCD file or recreate it using other answers from your Windows 8 disk.