Engine Mechanical problem
1995 Holden Apollo 4 cyl Two Wheel Drive Automatic 210000 miles

Been having a problem for the last few days whenever i started the car it would shake and sound like it was struggling. Went to start it yesterday morning and it starts to crank but doest turn over I have checked the spark plugs and also put in a new battery, the oil dipstick has a funny creamy brown sludge on it also
do you have any suggestions on how to go about diy fixing or is it time for the mechanic