Black screens at startup just after you pick a server and start entering the game can have a few causes.
1. Firewall, double check to make sure that it's allowing "dndclient.exe" outbound (and it's allowed to accept inbound connections) access to the internet.
2. Screen resolution set by the games default detection is not supported or is causing issues with the monitor,
- If it's opened/closed previously there should be a "userpreferences.ini" file in your "My Documents" (XP) or "Documents" (Vista) > "Dungeons and Dragons Online" folder if so open that file and make sure that under the [Display] section that the number following "Resolution=" matches what your Windows desktop screen resolution is set to.
- If it hasn't opened and closed before that file may not have been created, in that case try going into the options of the launcher (click the first button in the upper right corner on the launcher, the one with the single down-arrow on it) and in there under the "Repair" tab click to enable the "Reset game display settings" option, click Ok and try logging in again.
3. USB drivers or devices.
- If you have any USB devices, keyboards mice headsets etc try disconnecting and reconnecting them and resinstalling their drivers.
- If you have a "Saitek" or "Logitech" keyboard this can happen, also comes up with Wacom tablets as well.
4. Outdated or corrupted drivers for sound card or video cards
- Check with your PC maker, the card maker or (and in the case of many "onboard" sound cards) the motherboard manufacturer for the most updated drivers available
- Make sure DirectX is as updated as possible if needed via the link here.
If these options don't help you pin down the cause defintely
open a support request.