Vista home premium and explorer 8

Hello all,
wondered if anyone knew what would cause the file explorer to freeze when i try to view regular folders (mainly downloads, videos, documents, etc). I think it has something to do with the green loading bar on top. my hardware is a lenovo y510 with intel centrino core 2 duo with 2 gigs. i have 40 gigs free on 200 hard drive. don't know if the amout of files(size) per folder has any thing to do with it. it just shows the green bar on top as if it is loading but never loads. if i click another folder a blank window appears and to fix i must reboot. The only other things i notice is sometimes it tells me explorer.exe logoff sound is playing and can't shutdown. or SympTPEnh.exe (mouse)is still running. Read somewhere to shorten the sound of explorer log off and that seemed to help shutdown quicker. When i reboot everythings back to normal. Separately, every now and again when i startup it gets stuck at the black screen with the microsoft bar (again showing its loading but not). I just came back from the guys over in malware and got a clean bill of health yet somehow I feel like i have some sickness (some say its called vista). Don't know if anyone can help but would appreciate a word or two of encouragement