car won't start

i have a 1994 saturn, 1.9 twin cam. 175,000 miles. it was running fine until 2 weeks ago, then when i went to start it nothing, no noise, no clicking when i turn the key over, wait about 20 mins and then it would start and would continue for days. this happened about 4 times now it did it again and won't start at all. like i said turn the key over and nothing. is it the starter or what? if it is where is the starter located.