Keyboard sends wrong commands

I have a Dell 1545 Inspiron with Pentium Dual Core CPU.  When I'm typing along, suddenly it will send me to another screen entirely (something I didn't even have open, like a previous internet site I'd visited, for example) or at least kick me out of whatever I'm working on, e.g., email or Facebook.  When it kicks me out of the email I'm typing, sometimes Yahoo did not save everything I had typed and I have to remember what it was I wanted to say and re-type it.  A very frustrating problem!   It will also sometimes move my cursor (without my knowledge) to the internet browser bar and I suddenly realize whatever word I'm typing is going into that field instead of where I mean for it to go.  Please note, I have not set up any hot buttons, so I don't understand why this keeps happening. 

I have been experiencing this problem for several months now and am fed up!  Sometimes I can hit a key several times and nothing happens...like it doesn't recognize I'm pressing this letter.  Then I have to click somewhere else and go back and try again.  Sometimes it STILL doesn't work!  UGH!

When you respond, please note you are talking to someone who is not savvy when it comes to technical problem-solving, so please talk to me in complete sentences and explain things thoroughly.

Thanks!