If you have a Win ME disk, you could try a repair install, but ME is absolutely the worst version of Windows since 3.1. It is unstable and full of bugs. It was definitely a step backwards from 98SE, IMO. To make matters worse, XP came out very shortly after ME, and Microsoft promptly abandoned it.
I used to own a Win ME machine; I finally purchased an upgrade version of XP Home. Tremendous improvement. That is what I would recommend for you, too.
98SE is still usable, and worth repairing, especially for older hardware; ME is not worth the time, IMO.
If you go the XP route, back up your system first.
And, make sure you pay attention to the "audit" it will do of your system, listing the programs you currently have that will have problems running properly on XP.
If you have the hard drive space, the upgrade install will keep everything hanging around so you can, in effect, try out XP for awhile and still be able to revert to your ME system.
Once you decide you want to keep XP (and you will even though you may have to figure out what to do with those apps that don't work properly, etc.), you can tell Windows to delete the old files, and then you can convert the format of your hard drive from FAT32 to NTFS, and never look back.