There's 2 standby states.
S1 & S3.
Your computer is in S1 standby state which removes power to the HD's & peripherals, puts the monitor in standby and switches the CPU to standby. In this standby state the fans will continue to run.
S3 standby states put your computer into a deeper standby state by turning off everything inside your computer except the RAM. Read this link carefully
. There's an important section in the link about, possibly, setting the this setting only when installing Windows.
Some BIOS's, mainly the later PC's running at least Windows XP, let you change the standby state from S1 to S3 and this is something you need to check out and if it's available in your BIOS then you can force your computer to enter the deeper S3 standby mode.