Hi. I am sure it is very unpleasant experience when your PC crashed after you start few apps.
Crash happens for many reasons. I do not think it is because of number of applications but an issue with one application or completely different problem such as a problem with hardware, a virus etc.
If it is a problem with a particular application, you will see that whenever you attempt to use the application that creates the crash, the PC will crash irrespective of number of open applications. You can simply not use that application and solve your crash problem.
On the other hand, hardware issues mostly related to either improper loading of drivers or faulty hardware. If the crash is because of viruses, then also you want to install antivirus solutions, if you have not already done so.