Just like the other reply's, it can be your hard drive, but it may be others. I could try to pinpoint the root cause by answering these questions:
What OS are you using?
Do you have a HDD or a SSD?
How fast is your processor?
Is your OS and/or processor x86 or x64?
How much RAM do you have?
With info you give me to answer the questions above, I will (probably) be able to help you out with your problems. After all, I LIVE for computer hardware maintenance and repair.