Check Engine Light

I bought my car two days ago and it runs great and
I didn't get swindled out of money because my
brother went with me. I drove the car back home
and parked it. I have been sick but needed to go
run an errand, so I drove it just now and the check
engine light came on. I went to Autozone to get
some assistance diagnosing the problem but they
were rude and didn't even acknowledge me when I
came in and as soon as I asked my question,
before I could complete the sentence, they said
they can't check it because there are only two of
them working. Any ideas of what it might be? I
would appreciate any help. Thanks