My Dell inspirion 1720 laptop keyboard is locked. Anyone know how to unlock it

When you say locked, do you mean the numbers? Are any of your letter keys working? When you type on the right side of the keyboard do numbers pop up instead of letters?

If the numbers don't work, hithe Num Lk key in the right corner of keyboard.
If the arrows don't work, hold the Fn (blue letters) at the left bottom corner of keyboard while hitting the Num Lk key in right corner of keyboard.

If the letters don't work, you may have a bad keyboard (which is extremely common with dell), I have had to replace mine in less than a yr of buying the PC.
I have heard of some people holding down 2 keys and "unlocking" some component of the keyboard, the most common "key combination" is "a" & "z", I guess you could give this a shot!