Have you installed any antivirus on your Computer ? If not, I would suggest you to install one good antivirus program viz. Avast! pro antivirus or MSE on your computer and keep them updated. Alwayz scan every storage device while plugging-in.
You need not to run it for installing a new and fresh version of Windows. You just need to insert a boot disc and start booting from it. If you do not have a DISC, you could use a bootable USB for installation.
It seems like the OS version of your system a pirated copy. I would suggest you to install a new and fresh copy of Windows. Are you using any download manager for downloading ? If yes, try looking for the file in the default saving location.
What are the hardware configurations of your computer ? Win 7 requires at least 1 GB of RAM. If you are lacking it, please upgrade. Else i would suggest you to put a fresh install of it formatting the current installation.
I would suggest you to put a fresh install on your computer and keep it secure installing a good and latest version of an antivirus program viz. Avast! pro. Always scan external storage devices as plugged in. Install kaspersky internet security on your computer.
Install Google chrome on your system and set it as default browser. You can also disable IE on your computer as: Go to Control Panel-> Add/Remove Programs. In the left side you you need to click on Add/Remove Windows components and select internet explorer to disable.
Go to Properties of My Computer and click Advance tab. In the below section, click the button settings under the label Startup and Recovery. In the opening window you will see default operating system (you could change if you have dual boot). Check the first checkbox and change the...