Not Internet access and computer hanging on shut down

Since December I have had the following problem occur a few times without warning. You boot up as normal and everything loads quickly and the computer seems fine. But you cannot access the internet. When you open up any browser you just get a blank white screen. Yet the router lights are all lit and the network icon on the desktop shows internet access as normal.
The only solution is to either reboot or shut down and switch the computer on again. In both cases the computer goes to the shutdown screen and hangs. All obvious programs were closed before shutting down. So you have to switch the computer off at the wall socket. On booting up it now takes ages to go from the welcome screen to the desktop. During this time you have a blank black screen (no display) and extensive hard drive activity. After about a minute or so you get into windows but the various icons, clock etc them take ages to fully appear. After several more minutes everything has loaded but even after this if you click any application it takes time to open or load- even txt documents! The hard drive light is still busy. Finally everything calms down and the computer runs fine. And so far internet access is back. This type of occasion has happened a few times since it first happened and occured again today.
On the first occasion I cleaned up the hard drive and also did a scan disc on the next bootup. The scan showed nothing wrong- but when it rebooted and started windows automatically just before the welcome screen i got the message "cleaning up do not turn off computer". A message I have never seen before. This took about 10 minutes of again extensive hard drive activity before windows fully loaded.

It is a Dell XPS8300 computer i7-2600 Processor(3.40GHz,8MB) 8MB of RAM, 1GB AMD Radeon HD 6670
1
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510-10336 Sound Card : Sound Blaster X-Fi Xtreme Music Card
Sound Card : Sound Blaster X-Fi Xtreme Music Card

I have mcafee security centre installed.
I have not added or removed any software for a year or more apart from adding the Gopro studio in November. Nor updated or changed any drivers. The last windows updates was on the 15th Jan. No updates had occured before the other occasions. I did notice that the most recent macafee update was yesterday.
I am guessing that it is a piece of software that is preventing the computer from acccesing the net and preventing the computer from closing down correctly. Do you think macafee is a good suspect- though have had since I got the computer in mid 2011. Any other ideas?

cheers

bill

Kaktussoft said:

Disable firewall and virusscanner..... just to prove they are not the culprit. Post back results.
In command prompt:

Code:

ping  www.google.nl

4 sent , 4 received?

Thanks for both your comments & advice.
As this issue is currently random and intermittant I will try those ideas the next time it happens (as I am sure it will!) Doing the ping test today I got 4 sent and 4 received. But today so far the computer is behaving itself! I have one more year left on the sub for McAfee. But will move away from it when that runs out. Or sooner if I have more issues and I can clearly lay the blame with that software.

thanks