Welcome to JUST ANSWER small engines, let me try to help you !!
The engine can be seized. First remove the spark plug and look at the condition of it. Then tip mower up with the plug out and see if the engine can be turned by moving the blade. If not the engine is likely seized. Could be damage from being run low on oil on some other occasion or the oil could have become contaminated by gasoline and was too thin to lubricate the moving parts.
Let me know. Sorry.
Sure I also think that the engine is seized. If this so can the engine be repaired? or I need a new mower?
Your answer is not satisfactory