I have not filed taxes- what do I do now??

Ok- so I have been really slack and for the last 2 years I have not filed income taxes for the US. I did for the first 2 years I lived in the UK But then totally forgot about it.
What do I do now? I don't owe any taxes as I only work part-time and make about £10k a year. So clueless as where to start.
Can anyone help please?

When you last posted here in 2007 you were expecting, I would guess on your income you are due refunds from the IRS for refundable child tax credits (don't forget to report health in pregnacy grants, child  benefit, child trust funds etc) but do file and get all the refunds you are due.