I have to assume that your textbook gives an answer to this that you really ought to find. Different scholars have different ideas and you probably need to find the idea that your teacher will expect you to get from your textbook.
Different people have different ideas because it is very hard to say for sure why some idea or set of ideas got started. Some ideas are:
- Economic problems along with the Black Death led to social upheaval. This made it so that all the old values of society were called into question and could be changed.
- The fall of the Byzantine Empire caused scholars from that empire to flee to Western Europe. They brought with them classics of Greek thought that had been "lost" to Europe.
- Italy's social structure was changing and trade was bringing in new ideas.
So you see, there are many ideas about why the Renaissance began and I think you should find the one your teacher expects to see.
The Renaissance did not begin on a specific date and started at different times in different places.
One popular theory is that it started in Italy, more specifically Florence. One theory concludes that it began here because Florence was a republic. Men governed themselves and were in control of their own destiny. This gave rise to free thought and cultural growth. Italy was also very wealthy. During the middle ages Italy was a center of trade. Along with this large influx of people came a lot of new ideas and a lot of knowledge. Another reason is that there were a lot of ruins in Italy, especially Rome. This means that was a lot of art and art was cherished during the Renaissance.
The Economy was starting to spiral downwards