PLEASE HELP WITH MY COMPUTER!?

I Have A Dell Computer. Since Yesterday Afternoon My Computer Has Been Restarting On Its Own. & It Usually It Will Restart Every Few Minutes. Also, When I Try & Go To Facebook or Yahoo Mail The Full Page Doesnt Load. & When I Click On My Inbox It Wont Go To My Inbox.. I Have McAfee & McAfee Said We Recieved A Virus & That My Computer Is Now In "Enhanced Protection Mode". But, It Seems Like McAfee Isnt Working. Because It Hasnt Gotten Any Better Since Yesterday.