Spent way too much time trying to fix this today.

Switched off my N900 earlier today and went I switched it on it wouldn't boot. Shows the Nokia splash then 5 dots for a few seconds.

Discovered the flasher program and put it in R&D mode. At boot time it says:
No initfs \o/
Not sure if this is an error or an informational warning, as I later read that initfs is not used on N900.

Tried to flash the initfs but got a message about usb bulk write failing after 0 bytes.

Tried to flash the whole thing - a warm flash succeeded, but the N900 still wouldn't boot. Interestingly the full flash does not include initfs.

Tried a cold flash, but never got that to work - sits there saying:
Suitable USB device not found, waiting.

Think it's going back to the shop tomorrow for a replacement, but I was desperately trying to get my current one working as I didn't want to have to reconfigure everything, install apps etc. Failed miserably.

Any ideas? Did I miss something obvious?

I must say, the whole flash process is not particularly intuitive. I read a lot of forums before I got it to work, and I'm still not sure why the cold flash didn't work.