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The problem could also be viruses or other malware or one of many other possibilities, including excessive load at your ISP.

What kind of anti-virus/anti-spyware software are you running? What kind of network connection? What make/model is your PC? What size hard drive do you have? How much memory? What OS are you running? What's your web browser? The answers to all these questions will go a long way in helping determine the problem.

Check the memory.
You can test the memory by running Windows Memory Diagnostic that can be downloaded from http://oca.microsoft.com/en/windiag.asp. If problems are found check the steps below.

Test the Power Supply Unit.

Download Prime95.

http://www.mersenne.org/freesoft.htm

Prime95 is used to put your system at full load. You want your system at full load when checking your voltages to ensure your PSU is up to spec. The whole point is to make sure your PSU can handle what your system asks of it. When it is installed run it and go to Options and run the Torture Test. Run the Inplace FFTs (Max Power, Heat and some Ram).
If your PC restarts during this test you have a faulty Power Supply (PSU) and it will need replacing.

Download SpeedFan and check the Voltages and Temps while Prime95 is running.

http://www.almico.com/sfdownload.php

You will want your 12-volt rail to be within 11.52 to 12.48 during load. This means when you are running your cpu at 100% you do not want to drop below 11.52 or you may experience stability problems including but not limited to system restarts and Windows crashes. For the 5-volt rail, you want it to be within 4.8 to 5.2 to be within the 4% range. As for the 3.3 volt rail, you want it to be within 3.17 to 3.43

Video Memory Stress Test 1.4

http://www.majorgeeks.com/Video_Memory_Stress_Test__d5896.html

Reseat The Memory

Start by turninig off the power to the PC from the wall and remove the power lead from the PC. Remembering to ground yourself by getting into a position that will allow you to access the components without moving your feet and putting the back of your hand on the PSU after you have removed the PC's Cover. By not taking this precaution it is possible that you could inadvertantly cause damage to the PC from an electrostatic discharge. Disconnect the 20-24 pin power connector from the motherboard. Reinsert the 20-24 pin power connector to the motherboard. Remove the Memory and clean the golden edge of the cards with a soft rubber, remembering not to touch the golden edge.

Check with one stick at a time, remembering to disconnect the power from the PC.
Also check Capacitors around the CPU for swelling or bulging.

Note: A damaged or insufficiently charged internal battery can corrupt CMOS or BIOS settings. It can also cause all sorts of wierd things to happen.

Let us know how you get on.

Just think how many of us have multiple tabs/windows open while we're researching before we actually press that Submit button. If we "accidentally" click the back button to move back from the reply box, we might be posting something we don't want seen just yet! :0 I guess I better be a little more careful of what I say before I've said it and quit putting the first thing that comes to mind into the reply box! ]:)

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