You might miss relevant documents. Try synonyms and variations on words. Try with another search engine. Identify common words that are important to your search. Try to think of words that uniquely identify what you're looking for.
Some words are of little value, because they identify lots of documents.
The most distinctive a word, the more useful it will be for sharpening your search. The server you are trying to access may be too busy or temporarily down. Wait until a less busier time of the day. Avoid prime time hours. Knowledge of world geography and time zones comes in handy when jumping to other sites elsewhere in the world.