HI Bernie

The biggest failures are power supplies (This includes batteries) and HDD, (This applies no matter what OS you are running) now as you have been running the computer for about 10 years I presume you have changed the HDD at least twice, (If not do so immediately as you are living on seriously borrowed time) and it is probably time for another replacement, however I would recommend an SSD rather than a HDD. (NOTE- if your computer is that old that it only has an IDE connection on board then you are limited to a HDD)

Mainstream support for Windows 7 ended in 2015, with extended support ending in 2020, so now is the time to upgrade to Windows 10, (Although the free upgrade has supposedly finished, most uses who upgrade using the Win 10 upgrade feature on the Windows 10 download/disc report that it works fine without needing to buy a Win 10 licence https://www.zdnet.com/article/heres-how-you-can-still-get-a-free-windows-10-upgrade/) which gives you the option to check for any incompatible programs during the upgrade, however most programs will work natively, but if they don’t you can use compatibility mode, in the worst case scenario you can use Virtual Box to run Win 7 inside Win 10 (Both OSs run simultaneously) allowing all programs to run.

If you have never swapped a HDD before full details will be on the Dell website and if you get retail SSD it should come with all the necessary cables and software to copy the OS and files over.

Have fun

Bill