I saw a link around here somewhere where they found that in a good case you can run the AM1 cpu without a HSF. Setup linux or something on your Dell and try to sell it for a loss to recoup some of your money to put towards an ideal custom HTPC build. The Optiplex just looks like an unfeasible project at this point TBH.

I have the same conclusion unfortunately. According to my short experience with this contraption is really negative. Gas turbine like sound aside, I can only manage to make it run in a stable manner by opening up the cover fully. My home is about 28 degrees Celsius, and it generally shot itself down in a couple of hours at most, due to overheating. Even with the cover open, touching the PCU hurts your fingers.

It's definitely a lost case. Could be viable in a place like Alaska or Siberia maybe. 🤣

So what I did is this:

Second hand Intel Core2 Duo E8300 for 35TL
Second hand Asus P5G41T-M M LX for 85TL
New Frisby FC-S6035B 300W Slim Case for 110TL

230TL in total, which is about 85 USD. Considering that I will use HD5450 that I already bought, and RAM (2x2GB DDR3 HyperX 1166), DVD, HDD are coming from my existing stash, I think only loss is 35USD that I paid for GX280.

Only issue now is reactivating my Dell OEM Win7 pro that I already activated yesterday for GX280.

Here is a question: If I take the GX280 HDD (Win7 Pro activated and fully configured/updated) into the new PC, will it give me some unreasonable pain (both in booting into a new hardware environment and in activation)?

Just call Microsoft and tell them the motherboard in the Optiplex had a fiery death, you can get them to move OEM licences to new motherboards over and over again.
Its still the same computer... Well perhaps none of the parts are original but who cares 😜

Microsoft doesn't care, I buy dead computers with OEM licenses and resell them with a valid COA, the other day I sold a Toshbia laptop with an Acer Windows 7 COA attached, it activated just fine after calling MS phone support.

What they care about is this, how many comptuers are currently installed. The Phone System can't tell between OEM/Retail/Upgrade so unless you volunteer your fine.

If you want to keep the installation/files you can try to use sysprep on it. Works fine for Win 7 and up. You'll have to reactivate it, though.