Have you tried changing the boot device priority yet? (my above post)
If so, did that solve your first problem?
The shutting down problem is a weird one. Im not familiar with a way that the computer might have been set to hybernate or go into standby when you shut down via the start menu, so I would assume that that is not the case.
Your computer might be having trouble shutting down all of the programs and processes that it has to run. Giving it less work to do in that area might help.
Try this:
START
RUN
enter "msconfig"
under the "general" tab, select "Selective Startup"
uncheck the "load startup items" box
This will stop a lot of programs from starting up immediately when you sart the computer. Most of them also wont have to be shut down when you shut the computer down, so this might make things run more smoothly
If you go to the "startup" tab, you will see these programs.
All boxes should be unchecked, because of what I just told you to do
check the boxes corresponding to the things that you know you do want to start at startup and ask about things if you are unsure about them. Everything here can be reversed, so dont worry too much about permanantly causing a problem.
beyond that, if the people repairing your computer messed it up/ didnt repair it, then take it back and demand that it is fixed for free. Its ridicilous that a computer "professional" would accept money for a repair and return a computer in the shape that yours is in. If possible, get your money back and take it somewhere else