My computer is experiencing the following symptoms:
1. It keeps making crackling-popping sounds, mostly when loading.
2. The occasional slowing down.
3. My wireless strength used to reach up to 60, 70 or even 80! No it's barely at 50.
Some random ideas:
You can use the HijackThis utility (
http://www.trendsecure.com/portal/en-US/threat_analytics/hijackthis.php) to check if there are any weird processes running on your computer.
As for sounds and network strength, do you have any strong radiation sources very close to your computer, such as unshielded loudspeakers, mobile phones, fluorescent lamps or the like?
4. the weirdest, sometimes, my computer turn off but will still be running! The screen will turn black but the Fan and stuff will still be on.
I experienced something similar a couple of years ago, with the computer just spontaneously freezing up and turning off the monitor, but not shutting down down the computer itself. In my case it turned out to be caused by my motherboard having a too old version of the motherboard BIOS to fully handle my graphics card. After upgrading the BIOS to a more recent version that problem disappeared.
Though if you've just only recently gotten this problem without having done any changes to your computer hardware I doubt it's the same in your case.