[Solved] Guest Window keeps resizing to 300x150

[bootybay]

Since I re-installed Windows 7 and Virtual box I have this problem every time I start a guest.
The window keeps re-sizing to 300x150 and it looks like the picture I attached.

I can't even install a new guest if I don't select a ISO for the drive in the settings beforehand, because the selection window can't be seen and re-sizing the guest is not possible while it's open.
I don't seem to be able to find the right search terms to find a solution either.

I tried all 3 global display settings for 'Maximum Guest Screen Size' and nothing changed. 'Adjust Window Size' shortcut Host+A is re-sizing the window back to 300x150 as well.
Switching to Scaled Mode makes the window disappear completely.

I hope someone can help out.

[mpack]

Is this question about a problem with starting one guest, or is it about a problem creating new guests?

Your first paragraph seems to be talking about the former, your second paragraph seems to be talking about the latter. Please keep to one issue per topic. I will only address the first issue.

And what VirtualBox version is involved?

Speculative solution: make sure "Auto-resize guest display" is ticked in the "View" menu, then drag the window to the desired size.

[bootybay]

Version 4.3.26

I also installed Guest Additions to be able to use the 'Auto-resize guest display' and it makes the problem even clearer:
gfycat_com/BrownVeneratedChrysalis (Sorry can't post links yet. So please replace the _ with a .)

So it snaps back whenever the guest resolution is adjusting. So with Guest Additions whenever I resize the window while 'Auto-resize guest display' is enabled.
And without Guest Additions it happens when starting the guest, displaying boot logo, entering window etc...

[michaln]

Please attach a VBox.log from at least one affected VM.

[mhanor]

Read this thread

[mpack]

I have no idea what that offsite link was about, since I don't click offsite links. Please attach images and files locally. You don't need to post URLs.

As to mhanor's link, rather than read that entire thread, perhaps just try his central suggestion :-

Try running sfc /scannow in an elevated Command Prompt.

[bootybay]

The link was just small video that shows what exactly is happening. I paraphrased it anyway.

sfc /scannow fixed it. Thank you very much for your help.