There is no need to worry about compatability, the Inspiron 660 has a full driver set for Windows 7 64 bit and was initially sold with Windows 7 64 bit. The system is fully compatible.

Unfortunately Microsoft developed new measures in the BIOS settings which are likely to be the root cause of your problem these can thankfully be disabled.

For installation of Windows 7 follow A Clean Install of Windows 7 in my Windows Reinstallation Guide:

http://philipyip.wordpress.com/dell-community-forums/

Ensure that you Disable Secure Boot and UEFI (page 400). Also run the diagnostics (page 431).

He already has it installed ("After installing the Windows 7 Pro worked fine for a week"), so he should have already overcome the SecureBoot/UEFI mess.  It is more likely a driver issue - either drivers you did not install after the Windows 7 installation or drivers for devices you have since connected to the machine.

Which drivers did you install after installing Windows 7 and in what order?

Have you connected any devices to your computer (anything, including external drives, printers, etc.)?

What was/is the blue screen stop code?

Thanks for the reply mate!!!! Regarding compatabillity I had no doubt that the issue was with that, when I contacted the retalier for support that's the lame answer they gave me that i should have checked the compatabillity before buying, regarding the BIOS Secure Boot, I followed the guide to downgrade guide from the Dell website to the letter, all steps prior to installation of the 7 done including turning off the secure boot. Don't suppose you know if there's a recovert disc available to get from Dell and get back to Windows 8, Thanks mate!!!!!

Thanks for the reply!!!! I got al of the drivers from the website, to be safe i got them all, can't remember the order i installed though, and no external devices mate, just the usb stick i used to make the recovery media which it doesn't recognise or boot from. I no longer get the blue screen so i can't tell you mate, the computer no longer boots an OS it just comes up with insert a bootable devise to continue, I've tried to boot from the 7 disc and try a clean installion but it comes up with that it can't install, do you know if there's a recovery disc i could get to restore everything back to factory settings and windows 8 OS, Thanks mate!!!

You will need to phone Dell Technical Support to request it. This has had some limited results see this link for more information:

http://en.community.dell.com/support-forums/software-os/f/4677/t/19476992.aspx 

Windows 7 should work fine though, I don't know what happened with regards to your installation. I would try clean installation of Windows 7 again. Ensure that you install via BIOS press F12 at Startup when you see the Dell logo and then select your CD/DVD drive (with Windows 7 DVD). I would verify the BIOS settings, they shouldn't change but its worth a check to see if somehow secure boot/UEFI is enabled.

If you can boot from the OS DVD, there might be an issue with the hard drive. Sometimes brand new machines have defective hard drives; it's just the luck of the draw.

You might try swapping in a new hard drive.