System Inventory is an easy-to-use program which will generate a lengthy report on your PC's configuration.
This process takes quite some time, unfortunately: we're talking minutes, not seconds. It will finish eventually, though, so just leave System Inventory running while you get on with other things.
Once the program is ready then the report will pop up in your browser, where its information is divided into three sections.
The "Summary" covers the basics: computer name, IP and MAC address, CPU, Windows version, drives and so on.
The "Inventory Information" section provides more details on your hardware - RAM, BIOS, printers, network interfaces, drives and more - as well as some unusual operating system information, like "Registry Size".
But the "Software" section is far and away the most detailed, listing installed services, startup programs, running processes, installed programs, Windows components and patches.
While this is all fairly standard, System Inventory does have another useful trick it can play. Come back a month later, say, run the program again, and it'll generate a Recent Changes category, showing changes since the last report. And that could be very useful information if you're trying to find out why your system has started misbehaving recently.