Your PC should not require frequent reboots. My PCs stay on 24/7 and only get rebooted when absolutely necessary. My last PC was decommissioned just recently after as many years without a rebuild.
Okay, techie stuff coming up:
Run Task Manager in a corner while you do your normal work and note your CPU and memory usage. If your memory usage exceeds the amount you have, then your computer will get slow.
Run the Event Viewer (Start, Run, Eventvwr is one way) and look at the Application and System event logs. Look for lines which have a red ‘Error’ icon. If they’re plentiful, you’ve got a big problem, and report it back here.
Shut your machine down, open it up, and check that the heat sink on the CPU is firmly attached.