Keyboard and mouse not working

I bought a new pc from the pawnshop, and I believe when they bought it everything worked. I started up the pc and borrowed the keyboard and mouse from another computer and plugged them in, I know they were in the right slots at least once cus I tried them both. couldnt get anything from either.

My desktop and monitor are connected through a dvi cord. the monitor has the old 15 pin blue connection, but the pc has the blue 9 pin, but they both have dvi (i believe it was a custom built pc. so the dvi is through the graphics card). i can see the desktop fine.

what should i do? should i power it down and hook up the components before startup? help please.

 

nvm got it

 

Out of curiosity, what solved the problem? May be helpful to me/someone in the future.

 

Probably the fact he didn't have them plugged in before boot.
That solves the issue most of the times.

 

Ah, have had that issue before myself but not in years. Are they USB components or PS/2 ports?