Which Slot you have to short depends on your Motherboard. Search for yours in the post i previously posted.
Here an pic of one of those shortener:
http://blog.zorinaq.com/images/pcie-short-photo.jpgIt should be an solid one wire cable. If you can`t find it, ask your mum! Sometimes mums are using this kind for binding plants

@blueriver I read before, v2.8 would cause problems.
cgminer/bfgminer READMEs recommends to use AMD_APP_SDK-2.7
An clear uninstall of v2.8 via AMD Install Manager should be fine. Just dont save with reboots - windows need those a lot

- Windows reinstall shouldn`t be nessesary.
One more suggestion:
On my motherboard MSI Z77A-G45 there is a pci x1 pair between two x16 Slots. By using one of those, this disables the other one. I`m not sure, but i suppose in this case one graka shouldn`t be visible in the windows device manager at all, cause the disabling has to be an bios implemented chipset issue.
Try using different slots.