Why does my screen light only show picture when it wants to?

Well I have the galaxy s3 n the back light works I can press the lock button n it will light my buttons but it doesn't always show picture it does occasionally after I press the lock button and home button multiple time I can eventually get it to show picture ,also the charge port is lose n it makes it hard to charge have to place phone in certain spot for it to charge n I'm wondering what could be wrong with my phone yo cause these problems n is it fixable I would like to repair it if possible