solve simultaneous equations by matrix

I have 4 simultaneous equations as below

$\displaystyle

\begin{array}{l}

2I_1 + 2 - 1000I_3 = 0 \\

1000I_3 - 3000I_4 - 10 = 0 \\

0.003 - I_1 - I_2 = 0 \\

I_2 - I_3 - I_4 = 0 \\

\end{array}

$

I understand as far as putting them in matrix vector form, as below.

$\displaystyle

\left[ {\begin{array}{*{20}c}

{2000} & 0 & { - 1000} & 0 \\

0 & 0 & {1000} & { - 3000} \\

1 & 1 & 0 & 0 \\

0 & 1 & { - 1} & { - 1} \\

\end{array}} \right]\left[ {\begin{array}{*{20}c}

{I_1 } \\

{I_2 } \\

{I_3 } \\

{I_4 } \\

\end{array}} \right] = \left[ {\begin{array}{*{20}c}

{ - 2} \\

{10} \\

{0.003} \\

0 \\

\end{array}} \right]

$

However I do not understand how to solve. Does it have to be put in echelon form, if so how is it done I get loss with doing that. Could some please try and explain it to me. Unfortunately you will probably have to dumb is right down for me. (Worried) Thankyou.