High severity Vs Low priority:

e.g.:1  Login window

When we click on ok button the system is closing 
àShowstoppers.

e.g. :2 Keep on clicking on next button on each page at the 
10th page when we click on next button the window is not 
opening so HS-LP. Because users will not go up to 10th page

High severioty vs low priority

When we test the application during testing,at the 
time,suddenly system is hang it is high severioty.

When we test the application,if any spelling mistake or 
colour,or font size like that we may give the low priority.

High Severity and Low Priority bug:

ex: If an application is failing/crashing down when x(which 
is rare in real scenario) number of users are using it 
simultaneously. 

(This type of bug is given status as High severity as 
system crashing down is considered severe but low priority 
as the number of users using the application in real life 
scenario is very rare)

If from 500 customers 2 customers are failing to access 
100th page of site, then it is HIGH severioty but can be 
considered as LOW Priority sice out of 500 customers count 
of 2 is negligible.