When I turn on Computer, it powers up, but windows will not come up.  The Windows login screen comes up and the bar at bottom begins to scroll, but then the bar slows to a crawl and will not bring up windows (Windows XP).  Booting in safe mode will not work either.  I attempted to restore using System Restore In Microsoft Windows XP (Safe mode with Command Prompt), but it takes me to a blank blue screen and stays there.  This all started when I received a "svchost.exe application error".  Any ideas?.....