About a month ago, my Nokia N900 lost the virtual keyboard and auto cap function. At first, I thought I would be ok to use the slide keyboard, but now I am getting frustrated because I text more often now. I read some people have the same situation. I tried the reboot and original factory method but they didn't work.

Can someone please help me?

It happens to me from time to time.
What I do is the following. Clear the cache of microB. Go to the Setting and disable the virtual keyboard. Then enable it. Then reboot.
This always solve my problem.