Host of Problems

My computer has trouble shutting down. I'm running Windows Vista Ultimate 32 bit. For about a month now, it'll get all the way to the shutting down screen, then stay there all night. It used to be that if I manually logged off first, it would then shut down, but now it no longer shuts down unless I turn it off in the back. My other problem, is that whenever I have a dropdown menu, whether it is in the address bar of Mozilla, or the location bar of a folder, it just keeps blinking a lot. Also I have noticed a large decrease in the speed of my machine. Please I need some help.