I recently "bricked" my N900 by restoring a backup with backupmenu while having u-boot installed. Since that has happened twice now I highly suggest not to use both of them at once. If done though it is very likely that you'll end up with a device that is not only unable to boot, but also unable to be flashed to stock firmware since u-boot seems to prevent it from being recognized by the flasher tool. In this case even a cold flash (reinstalling the nolo bootloader) does not seem to work anymore. All this is very odd and should not happen, even more so since u-boot is installed in the kernel area and has nothing to do with the nolo bootloader. It did happen though and after spending hours trying to fix it, fearing that my precious N900 is lost forever, I thought I have to share my approach.

In order to save your phone you'll need of course the flasher tool and the latest fiasco and emmc image. You'll also need to know the hardware revision of your phone, but I'll get to that later. When you have everything set up the first thing you want to do is placing both image files in a separate folder since it'll get a bit messy. Then proceed with the following steps:


1. Unpack the contents of the fiasco image, you'll end up with several 2nd.bin-RX-51, secondary.bin-RX-51 and xloader.bin-RX-51 files all followed by several four-digit numbers. Important for us are the 2nd and secondary files. Open up a terminal and enter:
2. After you have done that you will have to find out the hardware revision of your N900. The hardware revision of your phone is also a four-digit number and it is somewhat hard to find out when your phone already "bricked". Go have a look at this thread http://talk.maemo.org/showthread.php?t=46314, you might be able to find it out this way.

3. When you have your revision number ready you need to find the appropriate 2nd and secondary bin file. A convenient way to do this on Linux machines is:
4. Next you want to flash your phone. All other tutorials on how to cold flash your N900 suggest that you flash the temporary nolo bootloader first and then the persistent one. However if you have the same problems I had this won't work. In order you get your N900 working again you have to flash the temporary nolo bootloader and the emmc image in one step. This must be done with super user rights:
Then immediately flash the persistent nolo bootloader...
...Immediately followed by the fiasco image:
I myself have no real explanation why it has to be done exactly this way I only know that this was the only way I was able to save my N900. If you followed all the steps your phone should reboot and you should be greeted by the first boot setup screen.

Good luck!