Computer randomly shuts down and has a hard time restarting

You buy a new laptop

Depends on the problem and the laptop, really. There are repair shops that will fix motherboard issues, particularly if you use a standard/common laptop like a MacBook or something.

The price of a motherboard repair merits a new laptop IMO.

You might be able to get it repaired under warranty

You might be able to get it repaired under warranty

This is a good idea

You might be able to get it repaired under warranty

Warranty expired in April unfortunately.

The price of a motherboard repair merits a new laptop IMO.

Again, it really depends on the computer in question. A liquid damaged macbook motherboard (which is probably one of the worst damages) can be repaired for a few hundred bucks, much less than the cost of a brand new one. You're a lot better off finding an independent repair place (never an Apple store, they are ripoffs) and trying to get it fixed, especially if you can find a no-fix-no-fee place.