Question why desktop system fan,processor fan even processor running in sleep mode(hdd gonna off)

[soourav]

when i click sleep my display and hdd gonna off but system fan, processor fan gonna running... when press any key it wake up in 5 sec. but i changed all settings about sleep. but it not take proper sleep too.
pc spec:
mercury h61tz mobo
Pentium g630
Nadia gt 610
4+2 ddr3 ram
500gb seagate
lg 22" ips led
450w iball smps

 

[PC Tailor]

What are you doing exactly to put it into sleep mode in the first place?