About 8 months ago my Windows XP laptop stopped being able to see FAT32 external drives when I plug them in... mostly. I will explain...
It happens with all my FAT32 drives, whether they be unpowered external hard drives, powered external hard drives, SDHC cards plugged directly into the machine's card reader, or SDHC cards plugged in via a separate USB card reader.
All of these drives/cards used to work fine on this machine. They all stopped working at about the same time.
NTFS volumes are not affected. If I plug in NTFS external drives they are recognized right away. I even have one external drive with two partitions on it, one is NTFS which is recognized, the other is FAT32, which is not recognized.
If I attach a FAT32 drive, then reboot, then the drive almost always becomes visible to the machine after the reboot.
Sometimes I can plug in a FAT32 drive and it works right away. Not often though. I'd say I get lucky more often with SDHC cards than hard drives. I'm developing a theory that I only get lucky with hard drives if I'm running Acronis Disk Director when I plug them in, though that usually doesn't work either - I need more data here, this may be a red herring. Getting lucky with a hard drive is really rare, usually I have to reboot.
When a FAT32 is recognized, either because I got lucky or because I rebooted, I can almost never safely disconnect it. It tells me "The device 'Generic volume' cannot be stopped right now. Try stopping the device again later". I can't seem to get around this. IIRC, I've tried closing every open window, and still no luck. Since I care about my data usually the only way to disconnect a FAT32 drive is to shut down the machine. As you can imagine, two reboots just to read a drive is getting pretty old...
When the machine fails to see a FAT32 drive it usually comes up with the appropriate drive letter and the words "Local Disk" in Windows Explorer instead of the correct partition name. If I click on it I get "J:\ is not accessible. The parameter is incorrect."
Before this problem arose I always clicked the "safely remove" button for everything, including SDHC cards where I think it's not necessary. I've known for a long time that this is the correct procedure for hard drives, so I don't think failing to do this was the cause of this problem (before someone asks :)
Any answers or suggestions most welcome.