Get 1.11 or 1.21, you won't break anything. Very slim chance of that nowadays

Have a little faith, there's not much you can do wrong (besides loading a beta version that is)
1.11: ftp://ftp.dlink.com/Gateway/dir655/Firmware/dir655_firmware_111.bin
1.21: ftp://ftp.dlink.com/Gateway/dir655/Firmware/dir655_firmware_121_no_securespot.zip
Sounds to me as a Windows networking issue. Please provide the router logs that show disconnections, if they're not there: have a look a your Windows networking config.
Do you have wired or wireless connection? If wired, do you use 1000 mbps with a different jumboframe setting?