If you want to record better sounding guitar tracks, getting an audio interface is the way to go, as others have mentioned.  You also want to think about shielding, interference, and turning off electrically noisy overhead lights. 

However, to say "You can't just use an adapter to plug your guitar directly into your laptop" isn't true.  I do this without a problem on my computers, its just not going to give you ideal signal levels. The  problem you might be seeing is that there is a mono-stereo mismatch between your mono guitar cable, your 1/4 to 1/8 inch adapter, and your input on the laptop.  I have both mono and stereo 1/4 to 1/8 adapters and laptops with both mono and stereo input jacks. Depending on my configuration, the input signal is reduced by half because of the way I've hooked it up, i.e. the incorrect conversion of a mono signal results in half of it being lost. 

At least, this is the issue that comes to mind when I read your  sentence, "when I plug the cable almost halfway of the adapter's body ... I can hear sound when I play and there's some loud buzzing sound involved."  There are likely multiple issues at play here.

1/4 to 1/8 jack problem
I'm using Windows XP and I hate the long start up time when I shut down and then turn on my laptop. However if I hibernate instead of shutting down it starts up much faster. Are there any harmful effects / disadvantages if I always hibernate whenever I'm done for the day instead of shutting down?
