Incomprehensible lags (Call of Duty 4: Modern Warfare)

Hello, forum users. The problem is this. For many years I played normally, but after the format of the computer it began to lag with a normal internet and a powerful computer. The lagometer jumps up to heaven several times for one second. What could it be from? :) If there is already such a question in the forum, sorry, I haven't scrolled through it :)