Macbook wont go to sleep

So here is my first problem with my Mac.

Simply just that when i hit the sleep button, it does not do anything.

Though I tried it again 5 minutes ago and about 3 minutes later the system did go to sleep. Only started happening past 2 days. Have not installed any new software and do not do anything that i did not do 8 weeks ago. I have only started re-using my Macbook 3 days ago when I came back. Wife used the Macbook a few times for basic internet. Beyond that, it was not used.

I have the late 2009 / early 2010 white macbook with Snow Leopard.
2.26ghz Intel core 2 duo and 2GB DDR3 1066 RAM.

2 areas to look - check Sleep settings in System Preferences in case they were accidentally changed and if all that is as you want it then perhaps a reset of the SMC is in order.