how can i fix the sound and some of the programs on my toshiba?

i have a toshiba satellite A105.
i've only had it for about 6 months and just one day out of the blue, the sound completely stopped working on some programs (i.e. windows media player, some games, etc.) but the start-up and shutdown sounds still play and some website sounds play, too. just no music, mp3s, etc. ive scanned everything on my computer with just about everything i have. ive used spyware programs, registry programs, anti-virus programs, etc. and my system should be completely clear and free. and another problem i have with my computer is that on some sites i go to (especially ones with a lot of graphics, etc.) my computer completely locks up. it does the same thing when i use windows media player, go to some websites, windows messenger live and yahoo instant messenger. i just want to know what is wrong with my computer and if anyone can help me out, ill be more than glad to try anything. thank you so much.