Viruses and other malware can slow down your computer as they mess around with everything from hijacking your browser to pushing advertising or phishing sites, to crashing your computer.
Spyware can also negatively affect a computer’s performance by installing additional software, redirecting web browser searches, changing computer settings, reducing connection speeds, changing the homepage or even completely disrupting network connection.
Faulty Hard Drive
A faulty hard drive can have bad sectors caused by shocks to the drive like closing the lid hard whilst the laptop is on or dropping the laptop.
Hard Drive 90% Full
When your hard drive gets to 90 percent full, that's when you see things start to move at a crawl. A full hard drive can also prevent a computer from starting up. It's best to not go over 50 percent to give your computer optimum performance.
Some programs take a lot of your computer's RAM to run – for example, programs that work with huge files such as photo or video editing software. A lot of people try to run Photoshop or some graphics-heavy program on an entry- or mid-level computer that can't handle it. Modern computers have a minimum of 4 gb ram but should have a minimum of 8 gb ram to start and run programs efficiently.
Sometimes the problem is not internal but external, can you feel air coming from the vent on your computer, if not, it is probably blocked with dust, this can prevent ventilation which cools the processor as it whirls away to run Photoshop, Spotify, Outlook and Skype. And nobody wants a hot computer – heat increases the likelihood of malfunctions, crashes and ultimately a dead computer.