In rainy days, the computer can't be turned on. Is it a power problem?

This is related to the motherboard being damp. Generally, the edge of the motherboard and dust accumulation are particularly prone to be affected with damp, which leads to local leakage of the circuit board, making the motherboard malfunction and unable to start.

Other reasons for humidity are micro-current leakage caused by the use of acidic flux and motherboard.

You can clean dust and use a hot air blower to remove moisture, so as to keep the use environment dry. You can also put the computer on a wet day and use the heat of the machine to remove moisture.