What is the exact make and model of your computer?
Recheck your connections again.
You could open your computer up, and make sure that all of you connections are secure. Check all the power cables are properly seated, check all the data cables are secured. You could also make sure the memory is completed seated in its slot.
Your manual may give you more details on what to check.
Always remember that a little static electricity can ruin components inside of your computer. You need to ensure you are properly grounded.About Static Electricity