I finally solved a problem I have struggled with for years and wanted to share with those that might be having the same issue.
I have the same problem that many Sony BDP-S300 (and variants) users have had. Over time, the player becomes fussier and fussier with disk quality until it won't even read most brand-new DVD's and Blu-Ray disks. We try cleaning the disks and sometimes that works. We try upgrading FW and most of the time it does not fix the problem.
The player says 'CLOSE' forever, then it finally says 'CAN'T PLAY' on the display and (I think) 'Cannot play this disk' on the TV. Then the player's screen goes dark and it just idles (it looks like it shuts off, but its still on).
Long story short, all I had to do was run a DVD lens cleaner (I actually used an ancient one made by Scotch / 3M for CD players) and now my Blu-Ray player reads two disks that it absolutely would not read until now. One of those was a standard DVD! I haven't tried any others yet but going from 0 for 2 to 2 for 2 is pretty convincing to me.
Unfortunately, I had already purchased a new player, but at least I found this out before I trashed the old unit!
Granted, this may not cure all probelms with the Sony BDP-S300, but I'm guessing it will cure many, as the symptoms are nearly identical in most cases.
Before you chuck it, clean it.