I understand that your having problems installing Windows* on your system and when it boots in to Windows* 7 it runs very slow.
At this point to be able to assist you better we will need your system configuration including processor model number, BIOS version, power supply and RAM memory part number. Also if you have any additional devices connected to the motherboard.
In regards to your inquire, I recommend you to do a fresh start, this means to get in BIOS, check the BIOS version and load the defaults with F9 then press F10 to save and ext.
If you are not running the latest BIOS go a head and update it. Here you can find the latest drivers and BIOS:
Then get in BIOS, under the configuration tab make sure that the SATA ports are set to Advanced Host Controller Interface (AHCI).
Save and exit.
Try a fresh install of the operating system, I you get any error messages please provide them.