When a new computer is bought as new it is covered by law as required by the Dept. of Consumer Affairs.
Dept.of Fair Trading
This covers things such as that the product will work as you had expected when purchased.
The computer retail market is both profitable and very competitive, and because of the fear of problems, a good
warranty is usually offered. Basically all components of the computer are covered by the individual manufacturer.
For instance the hard drive is probably covered for 5 years.
My experience would indicate that the parts suppliers are keen to honor the warranty, but some dificulties may
occur with the dealer.
A well known retailer will give a good deal, and should be the best to deal with, but will charge more for the unit.
Another problem with other retailers is that most large firms will replace a fairly new faulty unit with a new one, and
send the faulty unit away to be repaired. These repaired units are marketed at a bargain price, or are rebuilt into
another computer.
A trap for buyers is to return a computer as faulty when the problem is something that the user has done to the
software.
An example was a problem with a floppy drive which would sometimes be inaccessible . A second hand unit was
fitted and was OK at first but developed the same problem. The reason was found to be 'crosstalk' between cables
in the cabinet. Not the suppliers fault. A rearrangement of the cables fixed the problem. If this had been returned
under warranty, the supplier would have sent a big bill.
A corrupted program can appear to be a hardware fault. A dishonest dealer could also claim that the problem
was caused by the buyer.  Dealers, including big names, have ceased to trade.
For electronic equipment, most faults will occur within the first 100 hours, then if it lasts the next 2000 hours  a life
of about 70,000 hours can be expected.