external hard disk will not mount after PC connection

Hello,

My extern 300GB hard disk of my Mac was connected to a windows computer in order to place some large files on it. As mac user it is no problem to read any hard disk connected. For windows users however that system insists that no other disks can be read unless their addresses are changed to the windows standard. A partition address change was initiated with the result that nothing could be read. I then took a look at the external hard disk on the mac and discovered that it could no longer be mounted because of the change initiated by windows XP

Mac Disk Utility message:

first Aid Failed
Disk utility stopped verifying "disk1s1" because the following error was encountered: The unsderlying task reported failure on exit.

1 non HFS volume checked
Volume needs repair

I hope someone can suggest a repair for my extern hard disk.

What file system is the external drive?

The external drive was formatted into 4 partitions for the Mac system and now a partition has been created for Windows XP (NTFS,FAT 32,FAT16). This partition needs to be destroyed so that I can view my Mac data again.

Thanks for your interest and help.