Win7 won't enter sleep mode automatically

[crowTrobot]

Scenario:
My DX58SO's IOH fan is really loud and has a crazy bright LED so I decided to replace it with a quieter fan from an old 3.5-5.25 mount. Now I wanted to monitor my IOH temperatures when I run stress tests to see what temps I'm reaching so I installed Intel Control Desktop Centre as it is the only program I know that can monitor the NB (maybe there are others). Temps looked fine now I go to bed and wake up in the morning to notice that only my monitor went to sleep and my computer isn't in its normal sleep/hibernate state. I tried clicking on sleep mode to manually put it to sleep and it is working fine. I restarted and went to the bios to restore defaults to rule out motherboard overriding it and still won't enter sleep mode automatically. I disabled network wake and mouse wake and only have keyboard press wake the sleep and still nothing (this shouldn't really matter but all the google results I could find on this problem recommends this, so I had to rule it out).

Any one know what's wrong?

[Apoptosis]

Are both 4-pin fans?

[crowTrobot]

Thanks for replying.

The original fan was a 3 pin fan I attached to the motherboard's 4 pin onboard.

The replacement fan is a 2 pin fan I attached to the IDE power connector directly from the PSU. There is nothing attached to the motherboard's 4-pin right now where I took out the old fan.

EDIT:
I flashed the bios to the latest one and problem is gone. I still have no clear idea what happened though. It doesn't like not having anything connected to that IOH fan connector?