I have had Microsoft Silverlight installed for several months without a problem, 3 days ago I tried to use it and got message saying it was not available, it shows ok in program list, I removed it and tried to reinstall but it says it is already installed though it does not show in program list and Windows install clean up can't find it either - Any idea's please ?

Try this , re-build the index it's in control panel , index options , advanced , rebuild , If that does not do it try Runscanner or Autoruns , http://www.runscanner.net/ scan and look for silverlight entries , they will most probably be in red print , tick and fix .

Thanks Jack - I will try that..

I have tried both suggestions thanks but still the same -Runscanner could not find any silverlight files..

Well I think the installer uninstaller may have left some files or reg entries for silverlight still on the system , so http://support.microsoft.com/kb/290301 That's what this clean up utility is for .

Sorry Jack, but as I said to start with Windows cleanup utility can't find any Silverlight files to remove..

try to search for silverlight in your registry files, and see if deleting some of the silverlight entries helps. I know I had the same problem, don't remember the exact steps I took, I just recall deleting some of the entries manually, and then the installer replaced them and it worked ok. btw, don't just go crazy with the deleting, experiment slowly, entry by entry. how to format a computer format windows xp format windows vista