I can not locate the backslash key on the keyboard

on a standard keyboard should be key under backspace key

On most standard English keyboards the backslash key is located above the "Enter" or "Return" key. If your keyboard has been damaged, you can still copy and paste a backslash symbol that someone else has typed.

\ (backslash)
/ (forward slash)

Check the Regional Options of your pc, under the input tab

ASCII - Hold the Alt key and type 92 is \ backslash Alt - 47 is / forward slash.
You may have reassigned the keys. Go to Control Panel and reset in Region and Language > Keyboard.

the keyboards are set up on international standards and it is not usual to be able to configure a separate key for some other symbol

what is the keyboard type you are using?

How do I access the backslash key on an american keyboard

1) With your NUMLOCK on, hold the ALT key down and type 092 on your numeric keypad.  When you have NUMLOCK on, ALT and a 3-figure digit gives you special characters.  092 is the backslash on UK and Spanish keyboards, so hopefully it'll work for you.  If you get something different, you'll have to try different numbers until you find it

or 

2) In Start --> Programs --> Accessories there's a program called Character Map.  This gives you a list of available characters

or

3) copy and paste this one:  \

More than likely you have had something spilled into your keyboard and a full press is causing the stickyness to make a full connection with the above key. you have 2 options

1.> Just locate a local computer shop and ask for a used keyboard, shoudl be no more than 5$

2. If you choose this step it is important for you to follow it exactly..
Wash the keyboard in hot water in the bathtub.
Fill the bathtub with hot water so that you can immerse the keyboard in it fully and then shake vigorously for 30 seconds to 1 min

Take keyboard out of water and allow to drain. then shake again to help remove extra water.

Let dry for 48 hours minimum upside down.

Plug back in - all should be fixed, if not revert to solution 1

To get a backslash, you need to print the upper ascii character 92 (decimal). On most machines you can get upper ascii characters by holding down the Alt key and typing the decimal value on the numeric keypad. On the little IBM machine I'm typing this on, there is no numeric keypad, but if I switch on numlock (by doing shift-scroll-lock) the j-k-l keys become 1-2-3 etc. Now id I hold down Alt and type 92 (i.e.keys 9-k), this is what I get: \ Howzzat?.