You want something to catch the exception around the Double.parseDouble
for example.
while(num >= 0)
{
// input question after a character is inputted
System.out.println("Please input a number: ");
sumNumbers = myInput.readLine();
try{
num = Double.parseDouble (sumNumbers);
total = total + num;
System.out.println(total);
} catch(Exception e)
{
System.out.println("Please enter a proper number");
}
// ending statement
}