I restarted my N810 and it no longer recognized my mini SD card, which I've been using now for almost a year. I removed the card, inspected it, replaced it, and restarted the N810 again. No luck.

Any suggestions?

I would recommend trying it in your computer. If it reads it, I would copy all the files over, reformat the card, copy the files back and try again in your N810.

Check on another device or PC first. Perhaps the card is dead?
If it won't work anywhere you could try to reformat (not always possible)
Do you have another miniSD to check in the N810?

Thanks for the responses.

My computer won't recognize it either.

I don't have another miniSD to try on the N810

How do I format the card? If I format it will it delete what I have on it?

Thanks

Formatting WILL delete what is on the card.
In Windows Explorer, select the correct drive letter, right click and select format..
Use FAT32 (but not NTFS). MAKE SURE YOU HAVE THE CORRECT DRIVE LETTER !!!

There are a few places where you might not be able to go forward but this is worth a try. I would say your data is already gone.

Out of interest, what make and size is the card. We have had a lot of discussion here about our findings on quality etc.