I have spent 2 hours with no help online support sending me so many links that I could start a hot dog stand. Nothings worked. Finally, I figured out the extraction file and ran it. CS5 Extended installed, but it is so small (to see) on the screen it is basically unusable!!!!! Online support wants me to post to the forum and has no solutions! HELP!
Unfortunately UI Text Size Adjustment for high DPI displays is not available in CS5. It was first introduced in Photoshop CC - two versions later than CS5.
On CS5, the usual option is to reduce the monitor resolution to increase the size of text in the Photoshop UI.
If you're using Windows 10, you can try the steps listed by Phil DC at the link below to let Windows 10 try and solve the issue for you - albeit it's a bit of a compromise with some unavoidable blurry text.
Just to be clear: this is because you've got new tech (high definition screen) that did not exist when CS5 was made. Mixing generations of apps, systems and hardwares can be a bad idea, and lead to much pain. If you don't want to get on the merry go round of expensive updates, subscriptions, etc you can't pick and choose: keep an old, old computer and never replace or upgrade it. (One day that computer will fail and there will be hard/expensive decisions)/