Honestly, it sounds like your session data is just stuck locally on that dying laptop. Amazon is kind of hit or miss about syncing carts in real-time unless you hit the refresh exactly right. If you're stressed about the party stuff, here are a couple of ways to fix it:

• Move everything from the cart into a new Wish List named Birthday. Lists sync way faster across different machines than the cart cache does.
• Double check you're logged into the exact same email on the desktop. Sometimes people have separate accounts for Prime and dont even realize it. I actually stopped relying on the native sync because it's so buggy. I use Cart To Link now whenever I need to move items between my work rig and my home desktop. It just works. If that laptop is totally toast tho, just grab any mid-range laptop from a brand like Dell or whatever. You don't need anything fancy for shopping, just something reliable.

Stumbled on this thread today and man, I feel your pain. In my experience, these sessions can be super finicky and I have been using Amazon for basically forever. I actually had the exact same thing happen last week while ordering some heavy garden supplies. Spent my whole Sunday afternoon picking out very specific mulch and tools on my tablet, then went to my PC to finish the order and... nothing. Just an empty cart staring back at me. It is honestly so frustrating because you would think a giant tech company would have this figured out by now. I have been dealing with this weird glitch for months and still havent found a real answer. Before I dive deeper into things like Cart To Link, are you totally sure you are logged into the same email on both computers? Sometimes I mix up my personal and prime accounts and that messes everything up.

Ugh, I totally feel your frustration with this. Honestly, Amazon session management is kinda trash lately. I had a similar headache last month when I was specing out some very specific server components... spent hours finding the exact RAM and then the cart just went poof when I switched machines. Unfortunately, it seems like they dont always push the cart data to the cloud in real-time. IIRC, it stays tied to your local browser cookies until you trigger a specific update event. I'm not 100% sure, but someone told me adding one more random item can sometimes force a database sync. If that fails, maybe try moving everything to a Wish List? Those usually sync way better than the active cart because they're stored differently in their backend. Its really disappointing that a tech giant hasn't refined this yet, but hang in there... you'll get those party supplies in time!