Well, which kernel did you remove and how do you did it?

But much more important:
Did you flash the new kernel cleanly to the N900?

Background: The N900 was never intended to boot different kernels or OSs by its creators, it was developed over the years by some really smart guys. But the system has no automatic care-taking to make sure it will boot correctly.

There is some chances that taking out your battery for a minute or so, will reset some memory to bott cleanly afterwards. Also make sure your battery is loaded pretty good, because those reboot loop works hard on the battery.

If none of the above will change the corrupted state it is in, you might take the plunge and reflash according to the wiki about flashing the firmware http://wiki.maemo.org/Updating_the_tablet_firmware