Top most common computer problems ...

• Computer Virus/Spywares/ Malwares /Adwares:     This problem includes viruses, spyware, adware, trojan horses, worms, rootkits and any other piece of software designed to harm you or your computer without your consent. Removing a computer virus or spyware can be difficult without the help of malicious software removal tools. Some computer viruses and other unwanted software reinstall themselves after the viruses and spyware are detected and removed. Fortunately, by updating the computer and by using malicious software removal tools, We can help permanently remove unwanted software.

• Slow Computer: This is another top most problem.Computers are like new homes or apartments; if we don't make good use of our space and resources they get filled with clutter as time goes by. If your computer is slower than normal, we can often fix the problem simply by cleaning the hard disk of unwanted files. We can also install a firewall, anti-virus and anti-spyware tools, and schedule regular registry scans. External hard drives are great storage solutions for overtaxed CPU’s, and will help our computer run faster. We can use simple tuneup utilities and general preventive and regular maintenance as we do for all other problems to make our computer faster.

• Internet or Network Connectivity Issues: One day It gets connected but the next day its doesnot connect. Nothing has changed and we can't figure out easily too what to do. It may be internal and external problem for this also we have to keep our system uptodate and smooth so that we could figure out the problem easily.
• Dust and Cigarette Smoke: Computers generate static electrical charges that attract dust and cigarette smoke when present in the environment. We can use blower regularly as  a  general preventive and regular maintenance to make our computer faster.
• Hard Drive Failure: If we start hearing loud sounds that we were not hearing before, be scared because those sounds could be coming from our hard drive. 
• Dead Power Supply: When we press the power button and our computer gives no sign of life, and all the lights are absent, then the most likely cause is a power supply failure.
• Missing CD / DVD Drive or I/O Devices: If your CD/DVD drive disappeared, is not recognized by other applications, or just won't play or access your CDs or DVDs, we  are not alone everybody gets this type of problems.
• The Computer Won’t Start: A computer that suddenly shuts off or has difficulty starting up could have a failing power supply. Check that the computer is plugged into the power point properly and, if that doesn’t work, test the power point with another working device to confirm whether or not there is adequate power.
• The Screen is Blank: If the computer is on but the screen is blank, there may be an issue with the connection between the computer and the screen. First, check to see if the monitor is plugged into a power point and that the connection between the monitor and computer hard drive is secure. If the problem is on a laptop, then you may need to get a professional to fix it as some of the internal wires may be worn.
• Abnormally Functioning Operating System or Software:- If the operating system or other software is either unresponsive or is acting up, then try restarting your computer and run a virus scan. To avoid having this happen, install reliable anti-virus software.
• Windows Won’t Boot: If we are having troubles booting Windows, then we may have to reinstall it with the Windows recovery disk. Always remember dont format directly first try torepair, if not restore if then only not working just recover it with recovery CD if you have if then also it has not solved 
• The Screen is Frozen:- When our computer freezes, we may have no other option than to reboot and risk losing any unsaved work. Freezes can be a sign of insufficient ram, registry conflicts, corrupt or missing files, or spyware. First try to open task manager to kill or end that application but if this will not work, press and hold the power button until the computer turns off, then restart it and get to work cleaning up the system so that it doesn’t freeze again.
•  Slow Internet:To improve our Internet browser performance, we need to clear cookies and Internet temporary files frequently. In the Windows search bar, type ‘%temp%’ and hit enter to open the temporary files folder.
• Overheating:-If a computer case lacks a sufficient cooling system, then the computer’s components may start to generate excess heat during operation. To avoid our computer burning itself out, turn it off and let it rest if it’s getting hot. Additionally, we can check the fan to make sure it’s working properly.
• Dropped Internet Connections:- Dropped Internet connections can be very frustrating. Often the problem is simple and may be caused by a bad cable or phone line(in Adsl), which is easy to fix. More serious problems include viruses, a bad network card or modem, or a problem with the driver.