DSi Problem (Fatal Error)?

ok I have a dsi as you know it has v1.4.2 (I saw that is v1.4.3 out). The problem is, I start the DSi and ya know the health and safety screen, than I get the menu. When I click on ANY app: Camera, Sound, Settings, Games, 3DS transfer tool, I get error message which says: An error has occurred. Please press and hold the POWER on to turn the system off. Please refer to the Nintendo DSi Operations Manual for details. I left my DSi untouched for 4 days and than I turned on. It worked, Dsi browser, games, Camera, everything. I went to get a game and meanwhile I turned off the DSi. When I turned on I got the error screen again. I left for one day, again untouched and than turned on, it worked. I tried to update it, it goes to the 4th bar and it shows some error (I dont remember which) and it shuts down. Can anyone help me? Cheers, David