Wow ya having fun yet ? A couple of things here. You said the first time you tried the setup out you got to the boot screen then all went dark no beeps. and in your last post you mentioned you could check out your bios # so you must still get to the bios screen ?
Next would be the cpu and bios list is fron the uk and your profile Say's your in the states . The UK bios and the USA bios will be different Not really sure but I think really different. Your MB is for the US .
As for thermal paste as long as you can spread the paste evenly across the cooler it will work for you . I just wouldn't stress test the machine. If the CPU gets too hot it will auto turn itself off before any damage is done thats built into every system. So you can try your old CPU, You would have to reset your BIOS to factory spec first. Try that out with a ps2 keyboard.
Go get a live version of Ubunto to test this next part out. http://www.ubuntu.com/ burn it to a DVD. Now here's what I think is going on. If you got to the bios post your machine is working. What its not doing is reading something. A computer starts in the same way always. Hit the on switch power supply goes weeeee next is the ROM bios it checks to see what starting and goes OK we have this stuff to start in this order. so it would look to see what you have then the boot order then the OS. If your Bios is screwy it won't do that. Thats why you have the ability to reset the bios right of the MB Pull the battery and let it sit for a while couple of hours there's a ton of opion about that. I don't know how long it takes for the Capacitors to drain. That resets to factory specs. So does the pin method I'm just lazy . Replace your old cpu in the system making sure you spread what paste you have left evenly (BTW this stuff only 6 bucks for a life times worth ) Try it out when you get to the bios post hit del to get in and make sure the boot order is cd or dvd first then Hd save. If it starts but goes to black screen again insert the Ubuntu disk a windows disk would work just as well too but ubunto seems to do this better. restart your computer and let it boot off the dvd. If it starts then you have a software problem on your HD if it doesn't then its going to be a HArdware issue. Not as indepth as this should be but fron what I've read your smart enough to do this. Test it out let us know. We do love a good mystery I'm sure half the geeks in here are tell ing them selves something about this