@helmut85 - Howdy! Never be afraid to ask anything here. This is Donation Coder. We don't indulge in ridicule since we're all lifelong learners.
It's likely you have a non-SATA hard drive in your laptop.
While it's still possible to get an old-style PATA/ATA-6 drive, they're becoming expensive and difficult to find "in stock." Most drive manufacturers are phasing, or already have
phased them out. So while still possibly doable it's not very cost effective.
I can relate. I tend to keep and use PCs a lot longer than I really should. I had about a half dozen perfectly workable Compaq laptops with small drives (and RAM capacity) that I recently gave away because they just weren't worth keeping any more. Even with Linux running on them.
IMHO the best option would be to bite the bullet at this point and spring for an inexpensive new laptop - then use Microsoft's free easy transfer tool to migrate your data and settings over to it. Look for one on sale. Or get a name brand factory refurbished unit. You can some very good deals that way.
Seriously, a 10 year old laptop doesn't have that much service life left in it. And if you replace the drive, you just spent good money to put a brand new drive in an old machine - with a version of Windows that is about to go off support from Microsoft.
If, however, you still want to go with your original plan to get a new drive, give us the exact make and model of your laptop and we'll see what we can recommend to help you out.