Ok, so I've read a lot of different solutions covering a lot of different problems regarding similar products, but non of the solutions have worked for me.
Here it is:
I have an Iomega portable HD that is not seen anywhere in my computer. Not Disk Management, not Device Manager, nowhere. I have tried a different cable that is for my portable disk drive, and I've even tried plugging it into different USB ports. There are no problems with any of the USB drivers, they're all up-to-date. It was working fine yesterday and it works fine on my laptop.