The Windows Installer Service Could Not Be Accessed

Something's really wrong with my computer. If I try to save a download, the menu freezes up on me & I have to control alt delete to close it. When I do, I get a message that the program is waiting for an answer from me, but there is no window open with any request. Also, Spamfighter tried to do it's normal update & when Windows Installer gets to the end, it stops & gives the message that the Windows Installer Service could not be accessed. Does anyone have any idea what this might be? I'm very grateful for any assistance or advice.

 

For your installer errors see: http://support.microsoft.com/kb/315346