How much silver?

Just put my new system together, it has been a while since I built one, but I thought I had everything good, however the temp went up to like 110C right away, so I took the heat sink off twice and put a little more silver on it, but it is still staying at around 58-62C just idling.

I have a ZeroTherm fan installed, because of bad reviews about the one that comes with the CPU, along with the mobo fan and 3 case fans (front, back, side).

The CPU is an Intel dual core 8400. First I had just an EXTREMELY thin layer, as thin as I could get it, because I was worried about getting too much, but that didn't do anything.
Added a little more, which got it down to around 75C, and when I pulled it off I could see where the silver had only been touching the bottom of the heatsink on one corner.

Added a bit more, to be sure it was touching all over, so now down to 55C-62C or so, but don't know about putting more cause I don't want to overdo it, is there something else I'm missing?

Thanks in advance...

Very, very little is what you want. You want the thinest possible layer. The purpose of the thermal compound is to fill the microscopic voids in the metal surface of the CPU and cooler. You should be able to see though it if you put it on, clamp down the CPU and remove it.

I would recommend cleaning it with isopropyl alcohol and starting again.
By silver I assume Arctic silver?
Have you looked at their website, it has all the info you need

Arctic silverinstructions page

For an Intel dual core they suggest using a thin line of compound, in a particular direction, then let the pressure of your heatsink do the spreading.

Hope that helps

Thanks, so I guess that perhaps I need a different fan? The one I have I screwed all the way down, (it is a ZeroTherm) and if I put only and extremely thin layer of silver, (yes, ArcticSilver) then the bottom of the heatsink does not even touch the silver. If I put more that enables it to touch, but I guess that isn't as good...
Any suggestions for a more compatible heatsink? I've read several reviews which all said that the one which comes with the CPU is junk, which is why I didn't want to use it.

Is the fan you have suitable for your CPU?
Without any thermal paste the heatsink should sit on the heat spreader of the CPU, the paste only fills in the microscopic gaps.

What fan model do you have?

The fan is a ZEROtherm Nirvana NV120.
CPU is the Intel Core 2 Duo 8400.

As far as I know they should be compatible, but perhaps not for some reason... any ideas?

That's a model that can be used on both Intel and AMD chips... so the first thing to check is that you are using the correct fixing bracket.
You talked about screwing it to your mobo, so I guess you have the right one (AMD bracket uses clips).

I the bracket properly screwed to the heatsink?

Beyond this I would check for any warped parts on the heatsink or mobo. Or any clearance issues, memory getting in the way etc.

Yes, the bracket is on right, stuck to the back of the mobo with the fan screwed to it, there isn't anything that I can see getting in the way or anything, and it screws down fairly tight, the only thing I am not sure about is that the bottom of the heatsink is fairly flat, and the top of the cpu sits just slightly below the metal clamp/bracket that holds it in place, so that could be causing a gap, but that is just the way the mobo is made, so it doesn't seem likely, because if so then it would have a gap with probably any heatsink I chose...

Really at kind of a loss here, what harm will it do if I have too much silver?

According to everything I've read, (I checked before buying the thing) this heatsink should be perfectly compatible, so I'm not sure, maybe I have a defective one some way...but I don't see any spots that look warped or anything, so not sure what else could be wrong with it.

Using too much silver can be as harmful as not using any, basically the heat transfer will be too slow and cause overheating.

It maybe worthwhile checking the level of the heatsink. They do it using a razor blade in this REVIEW. Have a look through it and see how their installation compares with yours.
They show one image which shows the base as being slightly raised above the heat pipes

After that I'm a bit stumped... the fan is suitable for the CPU, what motherboard do you have?