windows not recognizing new additional hard drive

I have an e-Machine 633ids with Windows ME
Existing 15 gig hard drive. Additional 20 gig hard drive with external
enclosure

Windows isn't recognizing the hard additional drive. It isn't listed in "My
computer". Here's what I have so far: I'm not really sure if these are new or
existing but here goes:

System Properties - Device Manager

Disk Drives 1. Generic IDE Disk Type01 2. Generic NEC Floppy Disk 3. hpz 4.
IEEE-1284.4 COmpatible WDM Mass Storage Device (HPH11) 5. IEEE-1284.4 IOS
Port Driver (HPH11)

Hard Disk Controllers 1. Intel 82801AA Bus Master IDE Controller 2. Primary
IDE Controller (dual fifo) 3. Secondary IDE controller (dual fifo)

Storage device 1. ! USB Disk (has an exclamation point next to it)

Universal Serial Bus controllers 1.? Generic USB Hub (this has a
question mark beside it) 2. Intel(r) 82801AA USB Universal Host
Controller 3. USB Root Hub

Now the properties for USB Disk says "This device is either not
present, not working properly, or does not have all the drivers
installed. (Code 10.) and the properties for Universal Serial Bus
controllers 1. says it's working properly

When I did the plug and play thing I got a message that the file
usbmphlp.pdr couldn't be found. I found it in my Windows/Cab. I
tried udating drivers, but windows says all my drivers are up to
date. what is a .pdr file and what do I need to do with it? How can
I get my system to recognize this new hard drive?