My computer with Windows XP installed becomes very slow after I ran some heavy tasks at a time. (play a full 3D online game while extracting a 4GB RAR archive)
It freezes for about 200~500ms every few seconds, and this always happens if I do heavy tasks at once in my computer (for example, installing a program while playing games), and the lag remains permanently (even a reboot won't make it better) unless I repair-install the Windows.
Since I have a low-end computer:
Intel(R) Pentium(R) 4 CPU 2.00 GHz, 512 MB of RAM
ATI RADEON 9550 AGP 256 MB
And the only way I used everytime to fix this problem is by repair-installing my Windows XP. So that I won't lose any data or installed programs.
But I believe there's a better and faster way to fix this without repair-installing the Windows.