Further random thoughts:
1. Are you sure that the board is dry? Most of us would wait for some days after washing to attempt startup!
2. Clear the PRAM. To do this, turn on the machine and immediately and simultaneously press CMD Option P and R keys, keeping them down. If the machine is working properly, it should restart. This may or may not be needed, but it can do no harm and it is a common practice.
3. To start from the CD drive, the 840av does not, in my experience, respond to the usual holding down of the C key. You need instead to press the power on key, and then immediately and simultaneously press CMD Shift Option Delete, keeping the keys down until (hopefully) the machine boots from CD.
CMD is the key with the Apple on it.
1. Are you sure that the board is dry? Most of us would wait for some days after washing to attempt startup!
2. Clear the PRAM. To do this, turn on the machine and immediately and simultaneously press CMD Option P and R keys, keeping them down. If the machine is working properly, it should restart. This may or may not be needed, but it can do no harm and it is a common practice.
3. To start from the CD drive, the 840av does not, in my experience, respond to the usual holding down of the C key. You need instead to press the power on key, and then immediately and simultaneously press CMD Shift Option Delete, keeping the keys down until (hopefully) the machine boots from CD.
CMD is the key with the Apple on it.