Hi,
I'm surprised the shop didn't check your dump files but in any case we need to see your dump files in order to help you best. These are created at the time of bsod as long as the machine is configured to produce them. If you look in the main windows folder see if there's a folder marked 'Minidump'. If there is then read the link i post below and post the results.
If you do not find a folder marked 'Minidump' then you probably need to configure your machine to produce dump files.
Open the run application.
Type sysdm.cpl in the run box and click ok.
Look across the top of the system properties box for 'Advanced' and click that.
Look for 'Startup and Recovery' near the bottom and click 'settings'.
Near the bottom you'll see a drop down menu under the heading 'write debugging information'.
In the drop down menu choose ' small memory dump (256KB)'
Under 'small dump directory' make sure it says %SystemRoot%\Minidump.
Click ok and your good to go.
Once you know you have some dump files then read this thread and post the results:
How to ask for help with a BSOD problem In the meantime one thing you could try is pressing F8 whilst booting to get into the advanced boot options and look for 'Last good known configuration' and try that. It may get you back to a point where the system ran fine.