Viruses are not the only reason for your PC to run slow
The first thing that comes to mind or that a rookie ‘technician’ over the phone will diagnose is that you have a virus which will cause a ‘repair attempt’ that may be temporary but does not fix the source of the issue. Needless to say that it will happen after your warranty has expired and causing a repair to be extremely expensive or buying a new computer.

Don’t let this happen to your PC
Computers require an internal maintenance at least once a year

Having to get a desktop or laptop computer repaired can be a difficult and stressful situation. Whether you use your computer for work or have important documents and family photos in it, the last thing you want to do is leave it to a stranger for too long.
Aside from malware any other malicious attempt to harm your device, computers have two natural enemies: heat and humidity. Excessive heat accelerates the deterioration of your computer’s delicate components and humidity’s excessive moisture will settle inside your computer components causing failure or permanent damage.
Accumulation of dust and humidity
The cooling system vents and exhaust fans can block airflow inside the case, and even the thinnest layer of dust can raise the temperature of computer components.
The best way to avoid serious damage and extend the life of your device is to always have preventive and corrective maintenance services.

Laptops are, unfortunately, most affected by humidity and heat.
Due to its structure and portability feature, laptops require that all of its components to be extremely compacted causing dust accumulation which, in consequence, will end up blocking the vents where the heat is supposed to be expelled causing the raise in the internal temperature that can be felt while you as soon as you start using the device.
The symptoms begin with image display problems that most of the time can still be fixed if they are caught on time.
On the other hand, unattended these will eventually kill the motherboard.
Some other symptoms you may experience, are unexpected crashes, restarts, or shutdowns that end up causing loss of information, and damage to the Operating System or PC components.
There will be offers to get it fixed. In case it does get fixed, You should be aware that knowing how long that will last, is impossible. It could be a week or maybe 1 or more months.
Ignoring your computer overheating will cause a sudden shutdown at some point usually meaning that the graphics chip or video card is damaged and needs to be fixed, in the case of video chip and replaced, in case of video cards.
The first thing that comes to mind or that a rookie ‘technician’ over the phone will diagnose is that you have a virus that will cause a ‘repair attempt’ that may be temporary but does not fix the source of the issue. Needless to say, it will happen after your warranty has expired and causing a repair to be extremely expensive or buying a new computer.
