Isopropyl alcohol is safe to use on most PCBs. Don't get it on any mechanical parts though, like optical or hard drives, or fans. Use 70-99% isopropyl alcohol and use a swab to dab it on, then if debris needs to be cleaned off, use a soft cloth. Once the debris is clear, dab on a little bit of alcohol over the surfaces in question, then let it evaporate completely.
Don't get anhydrous alcohol, as pure chemicals can be dangerous and finicky to work with.