If the system is not stable after operating system installation, then there may be something wrong with one of the components ( may not be due to faulty components). Could be some components are not compatible with the system.
Make sure that the memory are supported and satisfy the memory requirements for this board.
Check the motherboard manual for minimum power requirements.
Try to set bios to default settings or try to clear the cmos by removing the board battery and put it back after about 15 minutes.
After installing operating system, Install the drivers properly, starting with chipset drivers, then audio, then the rest.
Note: if components are not compatible, system will always be unstable.
Hope this will be helpful to you.
I had a short night last night. I tried a lot of things.
One Problem is definitly the Intel AHCI Driver. For the installation last night I use an old SATA-Drive and the Windows7 Setuodriver and it runs perfect.
This night I will try to use my new Harddisk. I hope there will be no problem too.