Why is my income slowly falling?

So I'm starting to get discouraged here. I started affiliate marketing to make some side income while in school about 4 months ago selling computers for HP. I made a website, ran some ads, and I put in about a backlink a day on various sites when I get bored in class. Well on the first two days I started, I was making $30-40/day. Now that number has slowly depleted down to maybe $3-12/week. I want to just work higher but I am not sure what to do next, should I start with something new? If so could anyone point me in a direction?

The website is slow since it is new and I would have to say that probable 90% of sales right now come from PPC campaigns. I am just breaking even with the cost of the ads.

Get in something new. It Probably Ain't as profitable anymore! Theres some Hot niches you can still jump into right now and makes some good income!

As it is technology , maybe your adds for the tech your selling isnt new , up to date etc ?

may be you have dropped in search engine rankings? Also it can be the performance of your PPC campaigns. It can be many things, you have to check your log traffic and see what happened.

Check your search engine words. Maybe a new trend has come up

Competition increases by time... Trend falls...

Promote your website more and you will get back or even more than your earlier profit.

Promote more niches!

Don't put all your eggs in one basket

It always because you have more competitors, I recommend you to build more sites in different niches, and now you'll start build my backlinks for your website.