Submenu disappears when mouse hovers

I have looked at threads including suggested increasing z-index but that doesn’t work for me.I am using theme twentyten with own image. I have created a submenu but when I hover on menu the submenu appears with a gap between it and menu block. It disappears when mouse hovers over it. I have reinstalled WordPress software and theme to no avail. It did work previously for a while on previous installation. I have no plugins added yet.The only change that I can think of is that recent wampserver updates might have affected display (?????).

Thank You

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