Vista x64 reboot problems with XPS 710

I just received my new XPS 710 with XP Media Center Edition '05 today (specs in sig), and jumped right in to setting up a dual boot configuration with my copy of Vista Ultimate x64. Despite a few problems relating to 4GB of RAM (which were resolved by simply removing two sticks while installing Vista), everything appears to be working great. However, if I attempt to reboot the computer from Vista, upon restarting and bringing up the "DELL" logo screen, the short gray progress bar hangs about 1/4 of the way. To be clear, this is the screen which prompts you to enter BIOS or Boot Setup via the function keys, and the gray bar which "hangs" says "XPS 710" above it with the BIOS version below. I have upgraded the BIOS to version 1.4.1 but it did not help. The only way around the issue is to hold the power button in for a few seconds to shut the machine down completely, then I can power up the machine as normal with no problems. Rebooting from XP is also no problem. However, as you can imagine, this can become quite annoying when installing software. Is there anything I can do?