here is the fix https://us.battle.net/d3/en/forum/topic/6232743280 it works for me
GOT IT FIXED..!!
Battle.net Update Agent (Agent.exe) Issues
Issues with the Agent helper program may prevent Diablo III from installing or updating properly. If you notice your installation hanging at Updating Setup Files, or if you receive errors specific to Agent, try the following steps:
Bypass your router by plugging your computer's ethernet cable directly into your modem
Stop the installation process if it’s still running.
Wait for at least one minute. Ensure that Agent.exe no longer appears in the Processes tab of your Task Manager.
Restart the installation.
If that does not resolve the issue, delete the C:\ProgramData\Battle.net folder and try the installation again. The launcher will automatically rebuild this folder. If you cannot locate this folder, try these steps:
Click Start (Windows Key + Q in Windows 8)
Click Control Panel
If you are in Classic View:
Select Folder Options
Click the View tab
In Advanced Settings under Hidden files and folders, select Show hidden files, folders, and drives.
If you are in Category View:
Select Appearance and Personalization
In the Folder Options section, select Show hidden files and folders. This will bring up the Folder Options window.
Click on the View tab.
In the Advanced Settings section under Hidden files and folders, select Show hidden files, folders, and drives.
Try again to navigate to the proper folder:
Windows Vista/Windows 7/Windows 8: C:\ProgramData\Battle.net
Windows XP: Documents and Settings\All Users\Application Data
Delete the folder, then reattempt the installation.
axennero : i have to wait around 10 minutes to finish the launcher updates...so just put on a video to kill time hahaha
Edited by axennero#6490 on 2/7/2013 8:10 AM PST
I am having this issue as well and so is one of my friends, we have looked under the task manager and have not seen the agent.exe, the wow.exe, or any of them running after we close the updater, we let the updater run for about 2 hours and didn't move, but we aren't even getting to the actual launcher update we double click on the wow icon and than it brings up a white window saying launcher updateing and than a bar moves and sits at one spot at I would probably say about 75% and sits there forever....how can we fix this?
I have deleted the battle.net-files to make a rebuild, I have even succesfully reinstalled the entire game, but every time I try to open Diablo 3 it starts updating the blizzard launcher again. If I remove the battle.net-files again, then I am able to play it YES. The game-screen appears after asomewhat hesitant Update of the update agent (go figure). But only for once. Because if I quit the game and then try to reopen, the same problem persists. Quite irritating. Tried a lot of things already. Nothing helps. I thought my computer was giving me this trouble, not the game. But now I see that quite a percentage of people are having the same problems. I would like my credits back for this game, Blizzard-folk. The money spent isn't worth the troubleshooting I have experienced. Not by a loooooong shot...
PLEASE READ !!SOLUTION!!
Step 1st Download and install Advanced SystemCare 3 (suggestion by me) or another registrty cleaner
Step 2. Maintain Windows (scan & repear)
Step 3. Diagnose System (scan an repear)
Step 4. RESTART COMPUTER!!!
Step 5. Run as administrator Diablo 3 launcher!!
Step 6 ENJOY!!!
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