I can place jpg but not png images in Illustrator

Hi,
I have this problem with Illustrator recently: suddenly Illustrator refuses to accept png file.

All of my png images which have been embed disappeared (I opened the file and saw the pop-up that would show up when a linked image's location had changed) and when I tried to place/import them again nothing showed up. But when I place jpg instead then everything is file. After a few rounds of google search I tried reseting Preferences but it didn't solve the problem.

I would really appreciate it if someone can help me with the above issue.

Thank you!