Can not load Mad Moxxi and Zombie Island

Any help with the below problems would be greatly appreciated. I am desperate to figure this out so that I do not run into any problems with the General Knoxx DLC. I will gift/ buy someone a game on Steam if your solution works, yes I am that serious. Thanks for any help. Leave your STEAM account name in your posting.

1) I have purchased Borderlands through Steam. I have also purchased, downloaded, and activated Zombie Island and Mad Moxxi DLC through Steam. While playing Borderlands if I try to load Jacobs Cove (Zombie Island) or Mad Moxxi's Underdome the loading screen just keeps loading and does not go away (this is screen where there is a picture of the level and a random fact about the game is displayed at the bottom). If I press ALT-TAB and then go back into the game it asks for an Activation Key. I go into Steam and copy the activation key for the specific DLC and then paste it into the activation window then the message that comes up, about 3 minutes later, saying there is was an error activating and then the game crashes. In the past I have been able to play Zombie Island and Mad Moxxi with no problems at all, this started happening about 3 days ago, after not playing the game for a few weeks. I have the update for Borderlands that releases February 2, 2009.

I have used the "Verify integrity of game cache" option with 100% success in Steam for Borderlands. I have also used the "Defragment cache files" option. Below are two links to screenshots I get after putting in the Product code for Mad Moxxi and a screenshot of what happens when I click cancel and the game crashes.

2) Another problem I am having is that the introduction screens do not load. For the introduction 2K video and the Nvidia Video I just here audio, and then the main menu of the game loads. Other then two problems mention I am able to play every other aspect of Borderlands perfectly.

Since I have observed these problems I have uninstalled and then re-installed the game and I still have the same exact problems. My computers specifications are as follows, Windows 7 Ultimate 64 Bit, core 2 duo 2.2 ghz processor, 4 gigs ram, nividia 800m GTS.

You could activate the dlc directly. Go to your steam folder, then steamapps, common, borderlands, binaries

there you will see dlcsetup 1 and 2. The exe in those folders can be used to insert the key

Edit: Woah I misread big time. This solution could work for you too, just set Borderlands.exe to Windows XP SP3 compatibility. If after trying that it's not fixed you should also set DLCSetup.exe to WinXP Sp3 compatibility.