I am getting intermittent BSODs, which started during a scan, but now mainly come during boot-up....the last one had a: 0x000000DI error code / Driver IRQL not less or equal.
The only errors listed in Event Viewer worth noting on the shutdown dates are: ACPI BIOS is attempting to write to an illegal IO port address error, but my computer was having those regularly in mid May before the BSODs started.
Microsoft Error Reporting states: You received this message because a device driver installed on your computer caused Windows to stop unexpectedly.
I just found this in Device Manager:
on Microsoft ACPI-Compliant System
No drivers are installed for this device.
But when I click update drivers no update is found.
Please visit the manufacturer's website to download the drivers for your device. You can use google to find the manufacturer's website if you do not know it. In the support section download the drivers for your specific make and model of the device for your version of Windows.
Note: If the manufacturer only lists drivers for Windows XP and not for Windows Vista or Windows 7, that means the device is unsupported or incompatible with the unlisted operating systems.
If you do NOT know the make & model of your device you can Search by Vendor / Device code as shown in device manager.
In the device manager, for the device you need driver for, Right click properties for the device, go in details for the device driver.
You will see a code like per example VEN_8086&DEV_27D8&SUBSYS...
The VEN code means vendor and the DEV code means device: in this case the vendor is 8086 and the device is 27D8.
Once you have the two codes, go to www.pcidatabase.com.
Enter the two codes and you should get the name of your hardware. From there you can search for a driver download for your hardware.
Thank you for your helpful and detailed response nhasian. After further online investigation I'm not now sure that this unsupported device is the cause of the issue, but I will follow your advice if I am able to isolate the faulty driver.