The funny thing is, Ive tested the RAM, CPU, Hard Drive all independently. It was doing the Not Responding thing despite all the above, Including re-loading a new fresh OS on a New (and TESTED) Hard Drive.
The only thing I could add to what you said above was to start the machine in SAVE MODE, and see if it happens then. Then try it in SAFE MODE With Networking and compare both safe modes to your normal way of booting.
As your computer restarts - but BEFORE Windows launches, press F8.
To Remember which key to use, recite this little Jingle - (its so dumb and corny, you should never forget it now! ((heh))
Your F8 is in SAFE [mode]; or
F8(F-ATE) is SAFE
When running Windows 7, you may find it not responding due to an unresponsive program like Microsoft Outlook, web browser, antivirus, plug-in etc. or corrupt registry files, lack of minimum system requirements, damage drivers, fragmented files or hardware issue etc. Other these reasons, this problem can occur after you upgrade to Windows 7 from Windows Vista or earlier version. Check the steps given below and fix if your Windows 7 doesn't respond:
Step 1: Force shut down your Windows 7 computer when it's not responding. Be aware that a force shutdown may cause the unsaved data loss. Restart your computer and defragment your hard drive. Click the Start button> All Programs> Accessories> System Tools> Disk Defragment. Make sure that you are logged on as an administrator to your Windows 7 computer. Otherwise, you won't be able to defragment your hard disk.
Step 2: Run a full virus scan on your computer to make sure that it's not carrying any virus, spyware, bot infections. These can cause Windows 7 to hang. Open your antivirus program, update it first with the latest virus, malware definitions and then run a scan. Make sure that you are connected to the Internet; otherwise the updates won't go through. Wait for the scan to complete and then follow up. (Seel Also Virus Removal Support here)
Step 3: If you upgraded to Windows 7 from a previous version, make sure that your system meets minimum system requirements for the same. Lack of which can make your Windows 7 computer hang frequently or crash. If you are upgrading from Windows Vista, you needn't bother about system requirements that much except RAM or graphics card if you run heavy software and applications.
Step 4: If you upgraded from Windows XP to Windows 7, you will need to make sure that your computer meets them. Find out here Windows 7 system requirements. Corrupt drivers can be one of the main reasons for your Windows 7 computer to become unresponsive. Update drivers of your attached devices like router, printer, gaming console etc. either from the Microsoft Windows website or your manufacturer's website.
Step 5: Download Windows updates as well to make sure that your Windows 7 is running the latest, compatible patches, software, and programs. Click the Start button> All Programs> Windows Update. You should be logged on with admin rights to let the updates successfully install and work.
Step 6: You can also fix registry errors to make Windows 7 work again. If nothing works, clean install Windows 7 to fix any installation problems that it had to face during the procedure.