Thenl Microsoft started pushing Windows 10 onto it, filling the remaining space in the hard drive, and having their "GWX.exe" upgrade software stay resident in memory. I followed all the tips online on how to stop it, but Microsoft kept finding new ways to try to make me love them. Everything they did slowed my computer even more.
The correct thing to do would have been to wipe Windows from my laptop and install Linux. Instead, I bought a new laptop from Canada Computers, on sale because it was open-box. In addition to a regular hard drive, it has a small solid-state drive (SSD)!
Solid-state drives use flash memory to store data, instead of a spinning platter covered with magnetized rust. This is more energy efficient, and your computer can read the data much faster. If you install your operating system, program files, and frequently-accessed files on the SSD, your whole computer runs much faster.
Instead of ten minutes to boot, my computer is ready to go in under 12 seconds. Opening large programs such as OpenOffice used to take several minutes; now they also open in seconds.
SSDs are expensive, so you probably would want to store photos and infrequently-accessed files on a regular drive, until the price drops. But I highly recommend using SSDs for your operating system and program files.