After 15 minutes or so of playing my guitar on my Marshall Code 50...the display will grey out and I get no sound until I turn it off and then back on. It's good for another 10 minutes or so. What's up with that???
You could try a factory reset, if this does not help, please contact your dealer who can arrange for a engineer to look at the amp for you.
Hold down the AMP button while switching on the amp then hold down the STORE button to confirm the reset.