Maximised windows not filling screen

[duncan.oneil]

I've somehow hit a shortcut key or something while reaching across the
upside-down keyboard from the far side of my desk and now I have a
wide 'gutter' running down the left side of my desktop.

Maximised windows dont fill this space, and while normal windows can
be dragged into the space, they can't be extended into it
The task bar seems unaffected, and the start menu pops up as normal
(overlapping both the gutter space and the normal desktop space)
Additionally, I don't have a right-click menu in this space

I've searched around for answers and looked for what shortcut
combination I could have possibly hit, but come up with nothing so far
Anyone have any suggestion as to what I've done? Working with only
4/5ths of my full screen is really annoying

System is Vista Home Premium SP1 with all the latest updates

 

[PvdG42]

I've somehow hit a shortcut key or something while reaching across the
upside-down keyboard from the far side of my desk and now I have a
wide 'gutter' running down the left side of my desktop.

Maximised windows dont fill this space, and while normal windows can
be dragged into the space, they can't be extended into it
The task bar seems unaffected, and the start menu pops up as normal
(overlapping both the gutter space and the normal desktop space)
Additionally, I don't have a right-click menu in this space

I've searched around for answers and looked for what shortcut
combination I could have possibly hit, but come up with nothing so far
Anyone have any suggestion as to what I've done? Working with only
4/5ths of my full screen is really annoying

System is Vista Home Premium SP1 with all the latest updates

Any chance it's because the Sidebar has (somehow) had its "Always on Top"
property set on?
Right-click on the Sidebar, select Properties, then remove the check from
the "Sidebar is always on top... checkbox.