Newly installed microwave, model #JVM15440DM2WW. Read out started showing symbols and then flashes "please press clock". I did that with no results. NOTHING will work while symbols are showing. Unplugged the unit. Restarted, set the time on the clock and all seemed okey for about an hour, then the same read out appeared with the same results. Unit is now unplugged.

Depending on the make, just press the clock symbol once then press the numbers for the time and then press the clock symbol once again to set.

http://products.geappliances.com/appliance/gea-support-search-content?contentId=17872

Quoted from link above:

To set the clock on most GE microwaves:

1. With the microwave door closed, press CLOCK.
2. Touch number pads that reflect the time of day (1:45 would be 1, 4, 5).
3. On some newer models, indicate AM or PM for morning or evening.
4. Press CLOCK or START to lock in the time.

If you prefer not to display the time:
Disconnect the power for 30 seconds. After restoring power, do not set the clock. If your model has an ON/OFF clock display, you can choose not to have the time displayed. To choose this option, press the 0 pad for about three seconds. To Turn the display back on, press the 0 again.

To set the clock, press
"Clock"
once
or
"Timer/Clock"
twice
(depending
on your keypad)
.
The colon symbol (:) will flash.
Enter time of day.
The time appears
in the window; the colon continues
to flash.
Press
"Clock"
or
"Timer/Clock"
again - colon stops flashing; time of
day is set !

1. Open door
2. Press clock/Kitchen Timer button the display will show "0:00" with the hour"0" flashing.
3. Enter the correct hour by turning the potary dial. Enter 1-12
4. Press clock/Kitchen Timer button the display will show "0:00" with the minutes "00" flashing.
5. Enter the correct minutes by turning the potary dial. Enter 00-59
6. Press clock/Kitchen Timer. The colon will remain flashing.
7. Close the door.

"PF" on the display is an indication that your oven experienced a power interruption. Normally, the error code can be cleared by pressing the CLEAR/OFF button. You may have to reset the time. This is accomplished by pressing the CLOCK button, entering the time on the keypad, then pressing CLOCK again. If this does not clear your problem, please let me know. I hope this helps you.

According to the manual this is how to set clock.

To set the clock, press "Clock" once or "Timer/Clock" twice (depending on your keypad).
The colon symbol (:) will flash.
Enter time of day. The time appears in the window; the colon continues to flash.
Press "Clock" or "Timer/Clock" again - colon stops flashing; time of day is set.

If you need the manual it is on link below.

http://service.us.panasonic.com/OPERMANPDF/NNH624-SET%20UP.PDF

Good Luck

look for the clock or watch symbol on the keypad. When you press it, it will show you a 12 hour(normal time) or 24 hour(army time indication).Select the correct time by pushing the hour then minute buttons. Once that is done, press the clock symbol again whick accepts the setting.

press clear, press clock, enter time, press clock again.

The first thing to try is a "hard reset". Unplug it from the power line for a few minutes, plug it back in, set the clock, then try again.

Let us know if the hard reset doesn't fix it.

Please reply back with your brand and full model number.

Pressing "timer/clock" button 4 times turns on and off demo mode.