dell inspiron 620 will not boot after a storm went threw it tries but when windows logo appears it freeze up.changed power supply,memory,and hard drive out of inspiron 660 don't if motherboard will work or not
Judging by what you have already tried, your final two options are a friend CPU, or a fried motherboard (more likely).
If you have another LGA 1155 processor, or if your 660 has a LGA 1155 processor, swap processors and see if both computers run. If the 660 runs, but the 620 doesn't, then you have a fried motherboard and that will have to be replaced.
If your computer is still under warranty, they may cover it or be able to replace it for a cost.
If not, then a motherboard can be purchased from any reputable motherboard company such as Intel, Asus, MSI, etc. Just verify that all of your hardware is compatible with the new motherboard and the replacement should go off without a hitch.
If the computer came with Windows 7, you may run into a problem where Windows refuses to be used with a new motherboard and in that case you will have to contact Microsoft and explain to them that you had to change your motherboard due to damage before they give you a new activation key.