just horizontal lines on PM3

[hlava]

2 minutes after the finished workout PM3 display turned off, just few horizontal lines remained there.
there was no reaction on any button, neither on reset.

Then new batterries were replaced, left without power more than 2 hours but nothing helped.

There are still just horizontal lines at the monitor, no button reaction, neither reset helps.

Does anybody have any idea what should I do before I send it to the repair?

thenks
Peter