Windows Defender last update is: kb915597 However to access Win update,1st install: 890830
http://catalog.update.microsoft.com/v7/site/Search.aspx?q=890830
Also,to update Windows 7,make sure .NET is enabled in Win components/services..Plus,after all,download & install: windowsupdateagent-7.6-x86 get that thru Microsoft download center/search....A alternate web browser isn't the problem,try editing Internet Options,set all to default..If Windows fails,or to reset default installations,in run or cmd type: services.msc in msc,scroll to Win installer,double click,set to Auto start,start service,exit,do same in Win Modules..