Video stopped working

[Fletch]

I have a Emachines t6000. 64 bit, bone stock from the warehouse.
When I first received the PC it had no video and I had to send it RMA it. They replaced the motherboard.
When I got it back the video worked fine for several months.
My video problem started when the PC locked up while transferring video to disk. I had to power off the maching because it locked up. I let it set for several hours hoping it would recover but no luck. So, I powered it off by holding the power button, now when I power it up, no video. I replaced the video card with another good one and still no video. I called tech support and they informed me that I'm out of warranty. He did make a suggestion after I told him what happened. He said he thinks the video slot is fried.
I'm totally new to troubleshooting PC's and need some suggestions before I start digging into this thing.
From what I've read I need to take the motherboard out and set it on something non metallic and see if it will work that way. I don't think grounding is the problem and the case hasn't been opened but I'll try it since it did this before. If that doesn't pin point the problem, what should I try next. I have no diagnostic tools to check this thing out with.
Thanks in advance.

[Sylvander]

Download a copy of my diagnostic flowcharts from here
www.erniek.eclipse.co.uk/downloads/sylvanderdiags.zip
and print them to leaf through.
Begin on the STARTUP chart.

"now when I power it up, no video"
By this do you mean there is no display of white text on a black background, or any other display by the monitor?
The PC isn't "dead" is it?
Do you hear a single short beep at startup just before the point at which the monitor would normally begin to display?
If not, then you have NO POST.
The charts will probably direct you to the NO POST chart where you will be instructed to "Disconnect all peripherals..." [a "bare-bones boot"].

Here are more detailed instructions for that:
Install/connect only the power supply, MB, CPU, heatsink & fan, 1 stick of memory in the 1st slot, video card, monitor, case speaker, and power button, and make sure the power supply's voltage selector switch is set to the correct voltage and the PS connection to the MB is securely seated.

If there's still no beep, then check the CMOS battery for the correct voltage (3V).
If that's ok, then make sure the 'Clear CMOS' MB jumper is not in the 'Clear' position.
If the jumper is in the proper position, then turn off the power, disconnect the power cord, and clear CMOS either with the MB jumper or by removing the CMOS battery for at least 30 minutes.
If no luck with the above, then place the MB on a piece of cardboard. If there's now a beep & display, then the MB is shorting out when installed in the case. Check for a loose screw, standoff, etc., inside the case, and also remove any standoffs that do not line up with MB holes. If none is found, then remove all MB screws and metal standoffs, and install paper washers (manilla folder paper works good for this) between the MB and the screws/standoffs.

Let's see how that goes.