i hereby conclude what makes my desktop freezes is when i checked on "auto-hide the taskbar" setting on taskbar properties and used "turn off display after" setting.
so, these are things that might happen:
1. i disabled "auto-hide the taskbar" and disabled "turn off display after"
with / without any open programs
result: desktop fine
2. i enabled "auto-hide the taskbar" and disabled "turn off display after"
with / without any open programs
result: desktop fine
3. i disabled "auto-hide the taskbar" and enabled "turn off display after"
with / without any open programs
result: desktop fine
4. i enabled "auto-hide the taskbar" and enabled "turn off display after"
with a/some open program(s)
result...