How do I know my files or computer have been hacked?

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I've researched on this and found articles which did not answer some of my queries. I'm not a computer expert too, so my question might appear naive to people who are computer savvy. Right now, when I clicked on a site, there are times that it redirects me to a site I don't know of "akai.net" something. At times it also just can't find the website. Just now I found out that all my files in my desk top are shaded like someone is in the process of copying them. Can you help me out? How will I know if I've been hacked? what are the indications? Any help would be greatly appreciated. Thanks.