What is the size/capacity of the micro SD card?
If it is 4GB or larger, it requires a SD card reader that can handle the larger "SDHC" cards.
This is not the plastic adapter, it is the computer itself, or wherever you insert the full sized SD card adapter.
> i tried on all of my three computers (Microsoft 98, xp and vista) ...
Those are older computers. If the SD card reader is builtin to the computer/laptop, then they may not handle SDHC (>4GB) cards.
In general you will have fewer problems if you use 2GB or smaller SD cards (full sized for old Pleos, micro SD for PleoRB)
If you have a 4GB or larger card, it should work in the PleoRB, but you may need to buy a new USB adapter that handles SDHC cards.
Good luck