PC will not start

How about replacing the 2 ea, 2 GB sticks with a single 4 GB stick?

 

I'm not sure if it matters which slots you use. I happen to have a 780 here. I opened it up and noted there are 2 pairs of slots. I have one RAM stick in each pair. That means each RAM stick has an empty slot next to it.

Check out this video. This guy is adding (not replacing) RAM in his machine. The RAM placement in the video before the guy does the upgrade is the same as what's in my machine.

 

Shouldn't matter. I think those small form factor boxes still take desktop size RAM.

 

It can sometimes matter.
(Especially with a Dell)
Some of the small form computers use laptop size RAM instead of desktop size.
There seems to be no rhyme or reason as to which do and which don't.
I suggest you go to Dell website and scan your computer for it's hardware components.
Then post the results and we can better assist you.
I'm not at home right now so I'm unable to give you any links.

 

LOL
You are right, at that length, they are definitely desktop RAM.

I sub contracted for Dell for quite a few years and that's why I made the comment, "no rhyme or reason".
Dell likes to use leftover parts from previous models.
I've worked on small form PC 's that have desktop RAM and I've worked on the same exact models with different motherboards and laptop RAM is installed.

 

What's the price of the RAM upgrade?

 

I would run the Dell hardware scan on both computers before you make that decision.
Just because they are the same model, doesn't mean they have identical hardware.

 

You said you have a good 4 GB RAM board. It's the 2 GB RAM board that's the problem. I suggest replacing the faulty 2 GB board with a 4 GB board. You'll be looking at $19 + tax for the replacement RAM. If you purchase the computer for $100, you'll be spending about $80 more to get a spare RAM, a spare board, a spare optical and a spare power supply.

It's easy to swap out RAM and possibly a power supply. Would you be comfortable swapping out a system board?

btw: check eBay. Here's one for $28 + shipping. It has only 2GB RAM. So you'll need to still spend the $19 for the RAM upgrade. However, you'll have spare parts for $28 + shipping and as AllHeart stated not all Dells were the same. Ask the sellers if their computers use Desktop or Laptop RAM.
https://www.ebay.com/itm/175455030817?hash=item28d9ef4e21:gnQAAOSwJ-RjTuWj&amdata=enc:AQAHAAAA4HfIFOZ0bgDm12T3NLcOfKqVjHekgaJEpbt948c/Y9vfqPtfnWOqgp+ZhY3DGlKU9QTEtyrVzkaHQkclqPhLdaK1s+Izj0zs0P3Me/yGHIVSyZ8UdOWSph6PKWgpSNQ1fQv0K8GHINnXW7B8ZkwynKECD/C4zhHA6/6gspqVm/GIJb8yGJgOYxuwPVlgDozdbqwhchUQ3KuXYEd5PuKLFZh2Pq0sbnYcw9FHy9IM8I6upB1bRUm5FnJMhLvBb/8a6SN3e2SZgCXdslCqT3JKvX/MV1if/yGcF3GK6efzPMP8|tkp:Bk9SR87rgLWRYQ

 

Here's one for $50 including shipping. And the buyer is accepting offers so you may be able to get it for less than $50. It also has a hard drive. Looks like it has 2 ea, 4 GB RAM boards. However, I'd check with the seller to be sure. https://www.ebay.com/itm/394160332349?hash=item5bc5c95e3d:g:AKsAAOSwhN1izZcB&amdata=enc:AQAHAAAAoA22PSlF2Dhmadzw21N6G7ifdKmi3LEKrh09wHK1l6oXXghUJT47bQ/sep00nNBm/BwhGqAQsF2IYkNC7A1khg4WZQPw/Zl3eIWsAZksseY9z5KSHRzGcCRvemmTCatsLi+xkf7WXo33zsBES6K2f+BwDGG7Mg61pgI64x4LNTi5SzTBT4cB/S1lYD4PN+ITVNL94jvs4LYPYnEoZD9w8zA=|tkp:Bk9SR87rgLWRYQ

Simply put, your present computer isn't worth $100. I wouldn't put much $$ into it.

 

Yes, remove that 2 GB bar. We already know it's not reliable. Then install the 4 GB bar where the 2 GB bar was.