There are reports from a number of people that experienced some problems after installing one of the patches released by Microsoft, MS05-051 Vulnerabilities in MSDTC and COM+ Could Allow Remote Code Execution (902400).
Some of the problems reported are Inability to visit Windows Update, The Search tool in windows is not working, Symantec LiveUpdate is broken, After login you’ll get a blank screen with no icons, problems with Office, and SpySweeper is not working.
There might be also some other problems related to this patch.
If you are having problems with your system after installing the latest updates you might want to uninstall patch 902400, this seems to fix the problems for most people. In order to uninstall the patch go to Add/Remove Programs, check the “Show Updates” box and you will get the list of hotfixes. Select the 902400 hotfix and uninstall it.
Update: Microsoft posted an advisory on its web site with instruction of how to fix this problem