Laptop won't go into sleep mode

I have a Sony Vaio VPCEB32FM Windows 7 Home Premium 64 bit. I thought all of my problems were gone, but whenever I try put the computer into sleep mode with any button (the power button or from the start circle), it just turns black and won't go into sleep mode. The power button stays green instead of turning orange (sleep mode). Any help? Could it be a driver problem? Please don't suggest...