An IRQL NOT LESS OR EQUAL error is usually caused by a hardware driver or IRQ conflict. An IRQ is an interrupt request where a device requests time from the CPU. When different devices compete for the same IRQ, there are operating conflicts.
One of your devices may be in conflict with another device on your system. There is no one specific fix for this error. You will need to narrow it down by removing drivers or devices until it does not do it anymore. I would first try uninstalling your printer and card reader completely and then trying your external hard drive. Remove the software from Programs and Features and check Device Manager to make sure it is gone.
You may also be able to avoid removing devices by disabling them in Device Manager instead and then try to connect your USB device.
There is also a chance it could be related to a driver update for your sound card, video card or other device that you may have performed or even Windows Update performed.
I'm assuming this USB drive worked before and was assigned a drive letter? Did you check to make sure that it was not assigned a different letter this time?
You should look in Device Manager for any conflicts with your USB ports. See if you have a yellow question mark or exclamation point under the USB section. You can also right click on Universal Serial Bus controllers and select scan for hardware changes to see if it finds it.
Another thing you can do is go to a href="/support-categories/hardware/476-disk-management-drives" target="blank">Disk Management and see if your drive is listed there. If so you can assign it a drive letter if it doesn't have one.
I would also try this drive on another computer to make sure there isn't a problem with the drive itself. There is a chance that it has gone bad. Also make sure that your USB ports are working by plugging in a different USB device into the USB ports to make sure it is recognized by Windows.
Check and see if you have the USB device icon by the clock in the taskbar. Double click it and see if your device is listed in there. If not it may be another sign that it has gone bad.