Question Monitor no signal ?

[1a2a3a]

Hi, need some help here please.
monitor acer cb342ckc (a) connect via hdmi to hdmi to pc ASROCK J5005. Same monitor, also connect from laptop usb c to monitor usb c.
both can have display with I select input for hdmi and usb c respectively.
the problem comes in when I toggle out of hdmi to usb c and back to hdmi, the pc will not have signal. But when toggle back to usb c, everything is fine. Have to unplug everything and redo then hdmi get signal back from pc.
I tried removing usb c and just plug hdmi to pc. Works normally, but when I toggle input and let it recycle 1 round back to hdmi, no signal appear. It seems like when connected to pc, I cannot toggle out of the hdmi otherwise signal will be lost.

1. Tried on another monitor (b) or tv, no issue with toggling.
2. so I tried to change my pc to another laptop and hook up the laptop via hdmi, so 2 laptop connected to monitor (a) can toggle between hdmi and usb c no issue.

based on 1) seems like monitor issue. But based on 2) seems like pc issue. They seems to be contradicting which doesn’t make sense.
anyone has any idea what is going on?

 

[1a2a3a]

I just like to add some more information.


Pc - asrock j5005
monitor - Acer cb342ckc
previous monitor - Viewsonic va2719 qdh (no longer using, in fact sold)
tv - xiaomi 43

My previous setup was dual monitor - pc hdmi to Viewsonic, dvi convert to tv hdmi.
upon buying the Acer monitor I have changed to single monitor setup via pc hdmi to Acer.
I have occasionally connect my work laptop to Acer monitor via usb c laptop to usb c Acer.

Now here’s the problem. If I were to solely stick to hdmi on the pc there would be no issue. But whenever I toggle signal to usb c (dp-alt), there will be signal, but when I toggle back to hdmi from dp alt, there will be no signal.
I tried unplugging dp alt and just leave hdmi connected to the pc and do a dummy toggle, once it cycle back to hdmi, signal is lost again.
in order to get signal back, I have to off everything, unplugged everything, connect just hdmi and turn on pc. Or, connect pc via dvi-hdmi to tv and set the resolution for the Acer monitor via the tv before it’s working again.

So I tried connecting monitor hdmi to wife work laptop and monitor usb c to my work laptop, toggle between signal is working fine.
I can rule out monitor hdmi is faulty?

Next, since my pc does not have dp, I get a hdmi to dp converter to connect pc hdmi to monitor dp and laptop usb c to monitor usb c (the monitor has dp, dp alt, hdmi, hdmi). Toggling between signal is perfectly fine. But now, my pc unable to post bios splash screen when I turn on pc. The pc will boot straight into windows. It’s like bios splash screen is there but monitor does not receive any signal until it load into windows. Tried clear bios, cmos, turn off fast boot etc all didn’t work.
so I tried just connect pc directly via hdmi to tv hdmi without laptop and monitor, bios splash screen appear.
I mean wth?

so I either can’t have bios via my monitor or can’t toggle between work and my pc?
can anyone help me out with this?