You mean Vsx 405, right? Model numbers are senseless enough without typos.
Are you saying you DON'T have a remote? How did you ever set it up? There are several CU-VSX105 remotes available on eBay, one at $9.99 and expiring in a few minutes (17:12 PDT). If you get this in time you could snipe it at the last 10 seconds.
Many a Pioneer receiver will come up MUTING if it powered down Muting. It's not clear if you have been experiencing unwanted shut-downs. Unwanted Muting or any other command could well originate with an unintended remote control source. Mask the receiver so it can't see other I/R sources.