Though I appreciate your proper English, I'm not sure how to help you. Unless someone else can help, I'd suggest directing your question to Nintendo's webpage. Perhaps you have a warranty on it? My best guess would be a hardware failure, either a connection came unplugged, or the screen component failed. I'm not sure, again, I'd suggest directing your question to Nintendo.
You know what? Since you've asked your question nicely and properly (Which is rare on the internet), I'll direct you to the proper Nintendo support page for the DS Lite:
http://www.nintendo.com/consumer/systems/dslite/index.jsp
or
http://www.nintendo.com/consumer/repair/dslite_repair_home.jsp
I sincerely hope that you can fix your problem, and that others can learn from your example.
Ryan
Ryeguy, January 2009