Your question does not contain all the required information needed for us to help you. Please let us know which update is failing with the error code “800f0900”.
Follow the steps mentioned below to find the update:
1.Click the “Start” button.
2.Click on “Control Panel”.
3.Select the “View by” option that reads “Small icons”.
4.Select “Windows Update”
5.On the left pane select the option that reads “Update History”, this will show all the updates and those that have failed, along with the error code.
Adding to TaurArian’spost, you may follow the methods listed below to resolve the issue:
Check if the services related to the Windows update are started and set to automatic on the computer. Follow the steps mentioned below:
a.Click theStart button, and then, in the Search box, typeservices.msc, and then pressENTER.
Note: If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
b.In service list, look for the below mentioned services and make sure that service isstarted and set toautomatic. Background Intelligent Transfer Service Cryptographic Services Windows Update
Try installing each update manually and check. Visit the Microsoft download center and enter the KB number, download and later install the update available for the version of windows installed on the computer. http://www.microsoft.com/downloads/en/default.aspx
Try installing the updates in a clean boot state.
To help troubleshoot error messages and other issues, you can start Windows Vista by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate software conflicts.
Please follow “Step 1”, of the below mentioned link to start the computer in Clean Boot. Once the computer starts in clean boot state try installing the updates. After installing the updates, follow “Step 7” of the below mentioned link to start the