Back slash

Hello,

On an HP Probook 4420s with Win7, the backslash key turns itself on randomly and continues repeating itself.

This occurs often in Gmail, or in internet dialogue boxes, but also when using MSWord.

This problem has occurred from new purchase of the laptop. The backslash can be stopped by pressing the "esc" key on the original keyboard but not on the ancillary keyboard. The problem occurs whether or not I am using the anicllary keyboard (and screen).

Can anybody please offer a solution ?

Colin