Re: cannot update my nokia n900
 

There is the Settings application, scroll down to Product Information, look for the Version number to find your PR.
Anyway, as you are not able to update via the N900, i would suggest to contact Nokia Customer Care. Did you buy it in a local store or some online service, they should tell you about possible restrictions to download data? Do you have a PC for trying to update over the Nokia-Software, but i never used that application at all.
Depending on your computer knowledge you might consider reflashing http://wiki.maemo.org/Updating_the_tablet_firmware the whole thing.

Re: cannot update my nokia n900
 

I think i better contact with nokia customer care, thanks for help