#1 stack corruption in constructor

[zeromus]

WNDCLASSEX wndInputBox;
RECT rect;
memset(this, 0, sizeof(wndInputBox));

this isnt right. it should be

WNDCLASSEX wndInputBox;
RECT rect;

memset(wndInputBox, 0, sizeof(wndInputBox));

you may have meant to memset this also....

[zeromus]

indeed, you did, it seems that memset(this,0,sizeof(this)) is necessary