Dell won't start after cleaning fan

Since my Dell compact pc's fan sounded like a jet, I opened up the unit to clean it. I removed the heat sink unit (encased in plastic), sprayed all with the condensed air (from can) and put everything back, but now I get a blinking light in the front at the turn on/off button, it makes two long beeps, it seems to turn on, but nothing else will. Any suggestions? Thank you