active window to large for screen

Hiho- First try this- pull the taskbar down with the edge of mouse arrow till it disappears...relax, you can drag it back up with the mouse, too. You might be able to see the tabs for OK, etc now....using the TAB key on keyboard, press TAB and look for that OK button to get dark around the edge, which is the signal that it will be acted on when either clicked with the mouse or the ENTER key is pressed....try and remember what buttons showed the last time you could see the buttons....what position was the OK one in.....try different number of TAB presses to get to OK and then hit ENTER key to close and okay.
OR: If you can get to an empty spot of your desktop, you should be able to resize the desktop to a higher resolution (size) something like 800x600 is normal. It will want to restart to enter the changes....which should close the other window anyway....try that.
When you get situated- try to leave the screen size at 800x600 with large fonts.... if you use lower, with large fonts, the same thing is apt to happen with a lot of windows- been there myself.... some games also change the resolution and do not reset it to what you had.