Vista - Problems with Vista SP1

Ok, so I got a new laptop a few months ago which had Vista on it. I really
liked it at first and had no problems with it, but for about a week now some
problems have been developing. Firstly, it doesn't log on properly now,
instead just going to a black screen with the white mouse pointer on it, and
this seems to be getting worse by the day. At first it only took me about 3
attempts at logging on for it to work, but today it's taken me 11! As well as
this it doesn't shut down properly; it gets stuck on the "logging off" screen
and I have to turn it off manually using the power button on the laptop.
Also, now I can't access the task manager. I click on the button to get onto
it and the little green icon appears in the bottom right corner of the
screen, but nothing else happens. There are some other smaller things that
have happened such as it showing that I'm not connected to the internet when
I am, and programs that previously worked fine now just crash. These problems
all started happening on the same day and I've done nothing to set it off.
Someone please help!