HELP! My minimize, maximize and close top right hand side window icons disappear!

Can anybody offer any suggestions here. Each time I open a second or third file in CorelDraw x5, the windows seem to lose the top MIN, Max Close icons. You know the ones that sit at the top right of each window. Because of this I'm unable to close or edit the work. In fact NOTHING works. I'm running Windows 7 64 bit with a TON of memory.