Dell D620 cpu fan problem.

I got a refurbished D620 around Christmas time and I was really pleased with it as my spare computer. I noticed that the fan seemed to be on all the time in comparison to the other computers I've had, but it was quiet so it was no problem.

I've started using it for longer periods recently and one day it seemed that the fan wasn't on at all so I checked the temp with i8kfan and it was at 70C and the fan was off and showed no signs of coming on.

I then started to control the fan with i8kfan and just left it on slow all the time, then I changed the settings so that the fan would come on at different temps automatically so that the fan wouldn't be on all the time.

After trying to use my audio programs to record some music and finding that there was a problem with i8kfan causing dpc latency, I tried to see if I could put i8kfan back on manual fan control so that it wasn't causing these dpc latency spikes, like it did before when the fan was on slow all the time, and found that the program couldn't put the fan in slow mode, it just ran fast when I selected slow.

Also, whenever I stop i8kfan controlling the fan, the fan suddenly goes to high speed. It's like there's only two options for the fan now when its not on automatic fan control, off and high, whereas before it was coming on slow by itself and when that stopped happening I could put it on slow all the time.

Is there any way to find out why the fan won't come on without using i8kfan? Or why it only comes on at high speed when I relinquish control from i8kfan?

Sorry for this being really long but I wanted to give as much information about this problem as I could.