A slow computer is usually fixable and often cheaper to fix than to replace. Work through the causes in order, from free to paid.
Start with the free fixes
Try these first.
- Restart it, as many machines run for weeks
- Remove programs you never use
- Stop unneeded programs from starting with Windows
- Free up disk space and install pending updates
- Scan for unwanted software
Hardware that makes a difference
An old spinning hard drive is the most common cause of slowness. Swapping it for a solid state drive, and adding memory if it is low, transforms many older machines.
When to replace
If the machine is very old, cannot run current updates or the repair costs about the same as a new one, replacing it is the better use of money.