I don't have experience with u-bootpr1.3, only with Pali's u-boot. I had a more-or-less similar situation with a N900 where neither microUSB nor the microSD were working and Maemo didn't boot.

Using the U-boot console I was able to boot the kernel (which was stored in Mydocs) using a custom command line.

But you'd first need to know if you have a kernel image stored somewhere accessible (Pali's u-boot can fetch a kernel from Mydocs).

I guess the best is if you can post the exact output/description of what happens when you turn the N900 and try to boot Maemo. We can take it from there.