OS X V10.7 Lion :: All External Hard Drives Stopped Showing Up In Both Finder And Disk Utility?

i have this strange issue that occured just out of nowhere without me (knowingly) having contributed anything to it.yesterday i launched my iMac and my external firewire drive wasn't showing up in neither the finder nor on the desktop. i instantly thought about a hard drive crash, but soon tried other things to evaluate (or not) my guess. 

for instance, i unplugged the drive waited a few minutes before i plugged it in again. since this iomega drive is also equipped with a regular usb port i also switched cables and tried connecting it via the iMac usb sockets as well as via an usb hub without any luck. the drive still won't show up. so i launched the Disk Utility, to see if the drive needs some checking/repairing, but to my surprise it wasn't showing in Disk Utility either. 

thus far i only considered this to be an issue with only this particular external drive, but when i eventually switched on a 2nd external drive (this time an usb drive i use for Time Machine) that drive also refused to show up in either the Finder or the Disk Utility app. 

curious as i was, i then fired up a 3rd and 4th external drive and now had all 4 drives running at the same time. none of which were showing up, just as if they weren't even connected with the iMac. 

this strikes me as more than odd. i've heard about hard drive failures and crashes. they just occur over time. maybe and under some very strange coincidences it is possible that two external hard drives quit their jobs at the very same time, but seriously .... 4 of them?? i hardly think so. 

well, maybe it's the iMac's usb/firewire controller that's causing the trouble, i thought. but then again, my other connected devices (iPhone, iPad, Printer, Scanner, eyeTV) are functioning and get detected just fine as far as i can tell. 

i have no idea what's going on. i dismiss the idea of 4 external drives having crashed all at the same time just as much as i don't think that the iMac's usb/firewire controller has got any issues. re-formatting any of the 4 drives is out of the question and even if i'd consider such desperate measures, the Disk Utility wouldn't let me re-format anything anyhow, because the drives aren't listed there. i wish i could just use my Time Machine to resolve the issue but, as i mentioned earlier, i can't access the Time Machine because it also won't show up. 

Info:
iMac, Mac OS X (10.7.4)