Someone has recently given me an old Compaq iPAQ to see if anything could be done to make it workable, well... anyway... just to give it a try...
Change the OS from Traditional Chinese to English
Google a lot, and many people say using MTTY to upgrade the ROM - no success, with error message "...error connecting to Host".
Then, I found an easy way - simply download the English ROM from HP's website. Then, open the ".nbf" file with an editor like "UltraEdit" (download the trial version will do). Look at the very first line of the ".nbf" file, which is the ROM file. Change the language identifier text, e.g. "ENG", to the language in your current PDA, such as "CHT". This will fool the upgrade program that it's a Chinese ROM!
Now, run the upgrade program and follow the upgrade instructions. Done!
"error occured while formatting storage card folder (error code 31)
Read many posts on forums that iPAQ 3900 series not support 2GB SD card. In fact, in my test 2GB SD card is fully supported. Check if your card is formatted with FAT.
However, many have experienced the error code 31 when inserting their SD card into slot, including me. The slot is either unstable or simply stop reading any card. What I found out is that the slot has a pin crooked! Get a torch and see if this is the cause of your IPAQ not reading any SD card...
In my case, what I did is to open the iPAQ case and straighten the pin of the SD card slot. Now, it works again!!