cables don't just come loose unless the system has been dropped. even then its rare.
I was using my main system on friday night. playing a music video, surfing the web, my harddrive started clicking then bamm my mouse stopped moving and the whole system locked up. that was my 2nd WD SE 120GB hardrive that died 1 month out of warranty.
i would say out of all components in a computer harddrive's crap out the most.
most companies have a diagnostic utility on thiieir web page. you download it put it on a floppy or cd and run a full diag on your drive, to see if its failing.
im doing that at work right now on a seagate drive as we speak
luckily i didn't need anything on my drive, sure their was stuff i'd like to have. that is why you back up your sh**
It is very unlikely both drives failed at once.
It could be the cable I have seen it happen. Open the case reset the cables or better yet exchange them for known good cables.
It is possible the boot loader is messed up this is not uncommon on dual boot machines.