Mac/Time Machine won't find external HDD

Not sure why this is happening all of a sudden because nothing was changed recently to the Mac or the external HDD.

This Mac is:
Version 10.5.8
1.8GHz PowerPC G5
1.25 GB SDRAM

We had been using an external harddrive that was part data storage and part Time Machine backup. Last week Time Machine started giving me error messages. I restarted and now it won't find the external drive at all. Won't show up in Finder, Desktop, anywhere. When I open Disk Utility, the name of the drive shows up but when I click on it, "Verify Disk," "Repair Disk," etc are greyed out and I can't click on them. I tried to eject the disk from the Disk Utility but it said it could not be unmounted?

The external drive is on and whirring, the blue light is flashing. It's plugged into the same USB port it's been plugged into since we got it. What gives?

What happens if you go into Sys Prefs/Time Machine/Select Disk - can u select the HD in there?

If the drive is showing in Disk Utility make sure that you are clicking on the entire drive not one of the partitions. Also is the Time Machine drive connected directly to the computer? My Time Machine drive is an external drive connected to a Time Capsule. When I need to repair/examine the drive in Disk Utility I have to disconnect it from the Time Capsule and plug it directly into the Mac (USB in my case).

Collin: It's not showing up in Time Machine at all, just says "None" as my choice

Slydude: The partitions don't even show up in Disk Utility, just the generic name for the drive. It's plugged directly into a USB port on the back of the Mac.

helpabby said:

Not sure why this is happening all of a sudden because nothing was changed recently to the Mac or the external HDD.

We had been using an external harddrive that was part data storage and part Time Machine backup. Last week Time Machine started giving me error messages. I restarted and now it won't find the external drive at all. Won't show up in Finder, Desktop, anywhere. When I open Disk Utility, the name of the drive shows up but when I click on it, "Verify Disk," "Repair Disk," etc are greyed out and I can't click on them. I tried to eject the disk from the Disk Utility but it said it could not be unmounted?

Click to expand...

When u first set it up did you partition the Ext HDD into 2 areas?

Collin Bl said:

When u first set it up did you partition the Ext HDD into 2 areas?

Click to expand...

Yes we did; one for Time Machine backup and one for data that was moved from my boss' old computer onto this Mac (photos, docs, etc.). Everything was working smoothly until last week.

It seems to me you have covered the obvious so now for clutching at straws unless someone else can come up with a step. When i set up my wife's iMac to do a back up without telling her & she shut down the computer and then Ext HD would not mount. So taking casing off and removing multi pin plug but leaving power lead connected then applied power for 10 - 15 secs then shut down and reassemble. It was all back to normal then. If you cannot find anything else that might be worth trying.

I restarted the Mac again and after being on for a half hour it magically rediscovered the external drive and started doing a full backup of everything on the computer with Time Machine. I just let it do its thing. So the partitions are still there. If it happens again we're just going to get another hdd. Thanks again for everyone's help!

While it is being recognized and you have a backup run Disk Utility on the drive to see if there are any errors. You may be able to correct the errors now that the Mac can see the drive.