Intermittent FAN

There are two red flags in the post:
1. On-line gaming sites can be like banks. They are NOT there to 'help' you. They are there to take FROM you and may have installed an invisible process that hogs the CPU.
2. Virus - if it got through any current antivirus program, consider AVG-Free set to automatically update. I have never seen AVG fail to snag a virus the instant it tries to get into the system.

From there, my dated Toshiba laptop can suffer the same ill with a companion dramatic performance slowdown. It would be normal during a known intensive process such as a virus/adware scan. Absent that, Windows Task Manager may tell the story.

When the fan is acting up, press <CTL>-<ALT>-<DEL> to start Task Manager, click on the "Processes" tab and observe the CPU column. Find "System Idle Process" and watch it while observing the fan.

Under light load, the CPU value will trend in the 90% area, typically. The lower the prevailing number, the more demand other processes are putting on the system. It would be normal for the fan to run with a low "System Idle Process" value. If this is what is happening, then search the process list for the process that is putting demand on the CPU ... higher number is higher demand. You will note various processes randomly calling on the processor, so you are looking for one that is putting a heavy load on it all by itself. If you find one, 'Google' it for more information.

A really good possibility is a legitimate Windows XP process that has somehow gone 'rogue'. This has been the source of some recent loud complaints and I recall it to be one of the several instances of 'svchost.exe', a generic Windows module used in a variety of ways. I HAVE experienced it. When a heavy use process has been found, you can confirm its load on the CPU by clicking "Performance" and checking the CPU graphs. The rogue Windows process causes my graphs to go off the charts for no good reason. The only safe fix is to reboot the machine until such time as Microsoft finds out why this is happening.

If a high demand process is not found, some clever hackers can invoke a process that is invisible to the Taskmanager list, but its effect should still be visible in the CPU charts. In this case, the best hope for the average bear is that AVG or other very good virus/adware scanner will find it and remove it. I can think of no reason why a legitimate process should be hidden.

Finally, if a heavy process is not found and the CPU charts show low demand on the CPU yet the fan is constantly switching to HIGH, it is surely possible that the CPU temperature circuitry is intermittently and falsely reporting a high CPU temperature. Some systems will allow you to monitor reported temperature, which you can compare against fan operation. Exactly how on a given machine is different and usually found under the vendor's version of a 'tools' function. If it proves the sensor is faulty, it is unlikely that a tech can find and fix it on today's machine made motherboards.