Double pressing a key deletes my layer(s)?

Hi! I am a new computer graphics art student, so I am still new to photoshop. At school, we use Mactonish'es for everything, at home I use a Windows PC. However, there is this one problem that has constantly been nagging me for the last week. Whenever I double-press or hold down a button, it deletes my layer. For example, I want to use the magic wand tool, but when I press w it doesn't give me it right away, then when I press it again it just deletes my layer. Pressing it more deletes more layers. It also happens when I hold down "[" or "]" to change my brush size. How can I remove this feature?