It sounds like you have an assortment of problems.

Startup problems can be due to a bad driver, a misconfigured system, a
misbehaving startup program or service. Troubleshooting startup problems is
very similar to troubleshooting shutdown problems. A good shutdown
reference site can be found here: http://www.aumha.org.

Also, you are having some luck taking the machine completely offline and
letting it set for a while. There could be a heat problem (machine cools
and then can start correctly) or a physical problem with some of your
hardware. May need a local shop to track this down by testing components
individually.