Computer starting to freeze after 5 days!!

Hello,
I have had to re-install my system with my restore disk a lot of times... but not because of what is happening now...

I have Windows Vista SP1 (toshiba laptop)

Right now it only has the Norton (trail) that came with the restore disk...

I have been using my computer for like... 5 days or so now.... after i have restored it... it has gone BLAZING fast...

now... this is my problem after 5 days...

I start it up... i log in... im in...

i use it for maybe... a couple hours... then it starts kinda freezing... and then all the sudden... after 5 minutes of just a little freezing... it completely locks up... and all you can do is move around the mouse... then when you click... it says "Windows explorer is not responding" i click "Restart program" and then nothing works... so i just let it sit for hours and hours and hours... and it NEVER fixes itself... it just sits there with the little loading thing that Vista has... Why is this?

I still have (but didnt feel like installing again) Trend Micro Anti-Virus...
as well as Spy Sweeper... which i installed AFTER this problem happened...

I am really pissed because i cant seem to IM anyone or anything because IT JUST FREEZES!

what is it? is it a virus? is there any way i can fix it?

should i just go into "safe mode" and un-install "Norton Trail" and then install Webroot Spy Sweeper as well as Trend? (which i am going to try like right after i post this...)

PLEASE HELP ME!!! school starts in a couple weeks... and I need this computer...

THANKS!