Start with timing
Note whether the delay happens before sign-in, immediately after sign-in, while opening one program, or during everything. Startup-only slowness points in a different direction from a PC that freezes under load.
Check storage before installing cleaners
Low free space, a mechanical hard drive, a failing drive, or heavy disk activity can make the whole PC feel stuck. Avoid registry cleaners and one-click optimization tools; they can hide the real cause or add more unwanted software.
Look for a recent change
Windows updates, new startup apps, browser extensions, security software, and hardware changes are useful clues. Write down when the problem began and whether a restart temporarily helps.
When service makes sense
Arrange diagnosis when Task Manager shows unexplained heavy use, the PC freezes, storage makes unusual noises, error messages recur, or normal work is no longer reliable.