my friend suffered a similar problem but not becuz of the change of sim card but becuz when he turn off the phone he removed the battery before there was a total shutdown, meaning the closing animation was about to end when he remove the battery..

after switching sim, he can't turn it on and he brought it to the service center and they told him its a fault in k800i that when u remove the battery before a total shutdown there might be come corruption in the OS and there were already a few incident prior to my friend's...the phone was reflashed and all memory was lost but the phone is now ok again..