Problem with 10.5.6 update and External HD

[kpricester]

I've posted about this problem on the Apple Web site, but got nothing and haven't been able to find anyone else with the same problem. The other day, I installed the OS 10.5.6 update on my original Macbook (which is about a year old). My WD external hard drive was plugged in at the time via USB (I always have it plugged in). After the update successfully installed, my MB no longer recognized the external HD. I tried restarting both, didn't work. The HD doesn't even show up in the system profiler or disk utility. To make sure it wasn't a problem with the HD itself, I tried it on my roommate's Dell and it still works as well as my parent's iMac which is running OS 10.5.5 and it works just fine. I ran the disk utility while it was plugged into the iMac, but it didn't do anything. There are no updates to install for the HD for Mac users, I also checked with WD. Any help would be greatly appreciated.