We see this kind of post again, and again, and again:
"My (application or hardware) doe not work. Please help me!"
Alas, almost NO help can be provided to such requests. There can be many causes for incorrect operation. We simply cannot guess which of the many possible causes might fit your situation.
If you are having problems, here are some suggestions to get more prompt and more accurate help, Following these will also avoid the ire of "The Curmudgeons of the Freaks List" (tm).
1. Tell us WHAT you are trying to do. That is, please tell us (a) what you have done, (b) what you expected to happen, and (c) why you think that (a) should result in (b)!!
2. Provide us with CODE. Don't hand copy the code, but copy and paste, so that errors are preserved. Use the code buttons at the beginning and end of the code listing (works best if you click the code button, paste the code, then click the "end-code" button at the end). This will make it much easier to read and others will be more likely to look at it. If the code is big (maybe more than a 50-100 lines or so), reduce the code to a small version that demonstrates the same problem. Make sure that the code you provide COMPILES! PLEASE, tell us what compiler or assembler and what version you are using.
3. Tell us how the FUSES are set and what you use as a clock source.
4. Tell us what PROCESSOR you are using.
5. Tell us if you have tried to SIMULATE the operation of the code. If you did, tell us what you found.
6. Provide us with some DETAILED OBSERVATIONS about what it is or is not doing. This should relate to 1(b)(, above. "Doesn't work" covers a lot of territory! Is your LED off when it should be flashing, is your motor turning or not. Tell us what test equipment (volt meter, oscilloscope, etc) are available to you, what measurements you have actually made, and what the measurement results were.
7. If you have some suspicions about why it does not work, tell us what the evidence is for your diagnosis.
8. If you think that there is a hardware problem, provide a circuit diagram. Or, tell us what development board you are using and HOW you connect to it.
9. We understand that language is often a problem.. We understand that it is hard to understand specification sheets and application notes if you are not good at English [Note: its often not easy for those of us who speak English as our first language!]. If this is a major problem, please consider a board that uses your native language. When language is an issue, PLEASE ask your question the best way you can and tell us what you HAVE read.
10. PLEASE do NOT use shorthand "texting" language. Spell words out as real words and use a spellchecker. You will get faster and better help if you do. Also, "The Curmudgeons" will not make rude remarks about your post.
11. Words like "urgent", "ASAP", "I need it very quickly" and so forth do NOT get you good answers. All capitals, many question marks or exclamation marks don't help either. Asking the same question several times (duplicate post) will make a very bad impression.
Edited with suggestions from ArnoldB and JohanEkdahl.