Various errors when changing Photoshop document size to 300ppi

Hello, community.
I am trying to create a new file in Adobe Photoshop Elements 6, size A4.
When I tried to fix the document's size to 300 ppi, I found an error message saying:
A number between 1000 and 256.565 is required. Closest value inserted.

It then inserts 256.565. The file definitely seems too large. If I try to do anything to the file, the computer crashes, and sometimes displays the error message saying:
Move command could not be completed as file is too large.
I also tried to resize the image or create a new file, but I’m not allowed by Photoshop Elements to set the ppi at 300, and I'm always stuck in the above error message.
Can anyone suggest me a solution for this issue?
Thanks in advance.
