Nikon D7000 won't go below 1 shutter speed?

I have a Nikon D7000 that I have been using for a while now, I'm fairly familiar with it (enough to use it on Manual mode).

I usually take long exposure shots but want to now start taking shots that require a faster shutter speed (1/500 - 1/2000 etc) but for some reason my camera won't let me put a shutter speed below 1". Does any one know why?

Before you mention, the 'live video' thing is turned off, auto ISO is also turned off. I have searched the forums/D7000 book for a reason why but can't seem to find one.

I have a Nikon 18-55mm and Sigma 70-300mm lenses.

Professional guidance would be great, if you have an opinion on my choice of camera, experience or choice of lens I would also love it if you kept it to yourself!

Added (1). Two button reset does nothing.

when it is on M mode it displays the exposure time, how do I change the shutter speed in manual?

When you say you used to take long exposure shots, did you previously go below 1"?

You can try the "two button reset" but this generally just resets user settings, which may or may not resolve your problem.

Exposure time & Shutter speed are one and the same thing

In Manual Mode
Rotate the Main command dial to set shutter speed
(sub-command dial to set the f-stop)
http://www.dummies.com/how-to/content/nikon-d7000-for-dummies-cheat-sheet.html

See page 71 in your manual.