Here is the problem came to me: I changed a new MCU chip for my arduino uno, the new chip is also ATMEGA328P-PU, I bought it from RS, here is the link:https://sg.rs-online.com/web/p/microcontrollers/9222142/,after changing the chip, I can't uploading programs, and the led connected to pin 13 didn't blink, some topic in the forum says there is no bootloader, if it is true, what should i do and how to do to make this new chip have a bootloader; if not, what is the problem, how to fix it, thanks!
You will need a second Arduino or an ISP device to burn a bootloader.
As for anyone working with Arduino I recommend you invest $3 to $12 in an ISP device so you can refresh/update the bootloader if you ever feel like it. You can get a USBasp clone from the far east for well under $5 via eBay. Search for "USBasp", Buy It Now, and sort by "Price + Shipping: lowest first":
Most come with just a 10-pin ISP cable and the Arduino uses a 6-pin ISP connector so you will need an adapter. At or near the top of the list you should see adapters, two for $0.99. Add one of those to your cart. Then scroll down until you find the USBasp devices (little circuit board with USB plug at one end and 10-pin cable at the other). Currently the lowest price is $1.66+$0.11 shipping ($1.77 total). (For a couple dollars more you can get a fancy one with a plastic case but some clear packing tape or shrink tubing will protect the bare board well enough.) Add one of those to your cart. Check out and pay and you will have your devices in a few weeks.
If you want it faster you can look for an eBay vendor in your country. For example if I click on the eBay option for "Item Location: North America" the cheapest price for the USBasp jumps to $3.49 and another $3.53 for the 6-pin adapter. Still, $7.02 isn't bad and it should arrive in days instead of weeks. If you want it in two days and have Amazon Prime you can get one for $5-6 ($12 for one including the 6-pin adapter).