PC CPU bad? Or motherboard?

Trying to fix up a PC for a friend so don't know it's history. The CPU heatsink was plugged with lint so cleaned that out and cleaned and regreased the heatsink to CPU. PC is dead - no post, no video out, no activation of mouse or keyboard leds but fans run and it power supply goes on and off with front push button. CPU cooler is getting hot - not too hot to touch but hotter than expected. Tried a new power supply and got same result. CPU is AMD HD9500WCJ4BGD. Looking to get this going again without spending a much money if possible. Could pick up a used CPU for about $20. I have put together a number of PCs and have an electronics background but haven't had to do much troubleshooting to narrow down issues like this. Any thoughts on how likely the damage is CPU or motherboard or both?
What should I be checking? Core voltage on the mobo?

Any thoughts on how likely the damage is CPU or motherboard or both?
 
I have never had a CPU go bad.  I have though had issues with motherboards.  I did purchase a CPU once which was used for overclocking and it was bad from the get go and I returned it.
 
It sounds almost like the second power supply is bad.  If you have already checked it to function with another PC then it might be a bad capacitor.
 
Look closely as the capactors for bulging.  Sometimes just the little bulge will be problematic.  Sometimes too you see them in an exploded state leaking their guts.  I have had historical issues mostly with the old Intel Pentium D / dual core Pentium boards from a few years ago.  Never really seen this on my AMD based motherboards; but maybe I was lucky.
 
I did recently have an issue with a mITX commercial style board with a core duo on it.  It was using one of those plastic clip ons for the CPU heatsink and cooling fan (1U style).  One part was falling off.  The computer would start to boot then the CPU would get really hot and shut down the PC right away.  I was able to get to the bios once and noticed that the CPU temps were way way up there.
 
It is easy to fix but you have to remove the motherboard, de solder the old capacitor and replace it.  If the capacitor is really close to a bunch of stuff then it becomes a PITA.  There is a service which I have utilized out there that will replace all the caps on your motherboard and it is reasonably priced.  Thinking it is called bad caps dot com.

I would also suspect. The capacitors on the motherboard.
I have seen a few Dell and other brands with bad capacitors.
Use low ESR capacitors if you repair them or they will not last too long.
 
There is a whole forum devoted to bad capacitors in all kinds of devices. Like computers and TVs.
http://www.badcaps.net/forum/index.php?

Did you just try unlatching the cpu remove and replace to reseat and rewipe the contact surfaces?

There could also be a build up of dust under the cpu shorting things out.

It's been a long time since I built a PC but shouldn't there be error beeps from the bios on a failed startup? The bios is soldered to the motherboard so I think that the absence of beeps means a motherboard problem or power not getting to the board.
 
Mike.

Or maybe I should have asked - do you hear any beeps from the pc speaker on startup?

I know that electrolytic cap failure is a fairly common thing. I have replaced caps in other things - just did that on a router a couple weeks ago. Those type caps are often what goes first and limits life of products. But this motherboard has "solid conductive polymer" caps and I see no sign of any issues with them. Due to the type of caps I think cap failure is extremely unlikely.

Need to try removing parts (no extra boards so there aren't many) and see if I can get it to post. Will try reseating cpu. Also want to measure core voltage.

No beeps. That's the "no post" originally stated. Code is in bios but it requires the cpu to execute the code. I have seen one site stating that post will work without the cpu but that's impossible.

Yeah taking a multimeter to it will help. 
 
I am guessing you have disconnected all of the periferals (hard drive, floppy, video card...). 
 
I have had a bad hard drive suck the power off a motherboard.
 
Check too the memory sticks.  It will not post with no memory sticks but it should beep.
 
Let us know what happens or what you see.

Thanks Pete. I need to do a bit more checking - maybe later today or tomorrow.

Actually, the unit WILL do post without memory - thats what generates the beeps. It is just VERY limited and can't do many of the tests with no memory installed. checking for beeps with no memory is on the to do list.

Actually, the unit WILL do post without memory
 
Well if you have more than one memory stick try one at a time unless you need to have two memory sticks on the motherboard.  I have had one memory stick fry up and a few memory sticks over the years that would just not work.
 
Here too I have sometimes reseated memory thinking its ok but it is not. 

Also take a very close look at the pins in the ram slot, I have had pins short to each other once in a laptop.
 
Mike.

Pete,
 
My point about post without RAM was a general comment, not about my particular case - I didn't word it very well and think I gave the wrong impression.  My point was that without RAM the POST does a few of its checks and beeps, if it has RAM it does more.  For my current case the unit doesn't beep at all when powered up. 
I need to check what happens without any RAM.

Not a huge deal but I was trying to address your statement: It will not post with no memory sticks
which is not technically correct.

Understood Jim.

I think Larry hit on the issue. I reseated the cpu and pulled out memory and disconnected the drive. Got a post beep. Put things back in one at a time and continues to get post beeps. Ended up with everything reassembled and a working PC. Very surprising.