Inspiron 1525 power problems (doesn't boot).

My problem is now on this video:

At first it started to shut down than I couldn't turn it on. I believed that I fried it so I changed the CPU, motherboard and DC jack. But the real problem was that the charger's wire was broken so I replaced the wire.

Then I turned it on with the new parts once and with the old parts 2 times. Each was only for a few minutes to see if it works well.

Finally the problem occured with the old and new parts, too.

I applied thermal grease and changed the thermal pad but it didn't solve the problem.