I can't see my external FAT32 drive

I have an 80GB hard drive that used to be in my MacBook Pro until I replaced it with a 320GB. All went well. Could see, read, and write to it.

I put it in an OWC enclosure and reformatted it as a MSDOS FAT32 as a single partition using Disk Utility v. 11.1 on Mac OS X 10.5.8. All seemed to go well. The drive mounted, I could see it in the Finder.

I put it into a Windows 7 machine and copied some files onto it. About 25 GB worth. Can see it and read and write to it in the Win7 machine.

Now it does not mount on the MacBook Pro, Disk Utility does not even see it.

Is there a command in terminal that will let me see it and reformat it again? The files are safe somewhere else but I would like a working drive.

Again, it does mount, read and write in the Win7 machine but the MacBook Pro, OS 10.5.8 and Disk Utility 11.1 cannot see it at all.

Thanks in advance,

Sue