I can not download, save and delete file from my PC

this could be masses of things it sounds like you dont have access to things on your computer. Is it a personal computer you have at home or one in the office? depending on the above, you may not have necessary security permssions to do what you want. most organisations make it so you cant install anything on the C drive

If your using Linux, you need to have one user with access to the hard disk, usually root user. Although that shouldn't disallow you from downloading. You may have been hacked.

Check if the account you are logging in has the administrator privileges. With other types of accounts you have the restrictions on the operations with your HDD. Do you get any error message, when you try to operate files?

Its probably a Virus or a spyware. Check your anti virus,plus install and run Anti Spyware like SPYBOT search and destroy. If nothing works, Format your machine which can be the last resort .... Try to check if you anti virus is good enough, use NOD32 or BITDEFENDER or AVG .Hope it helps...Best of luck buddy !

Reinstall your Operating System. It sounds like a hijacker took over your pc.

get in the safe mode. stop abnormal services or stop services running out your OS. you can active Hijackthis software.