you should be getting a power supply in the $50-$70 price range.
http://www.newegg.com/Product/ProductList.asp?N=2010320058+4026&Submit=ENE&SubCategory=58
if you have tried many different DVDs and it still does it, then i would say that a lever has been damaged, and is unable to pick the DVD up enough, or unable to hold it up.
Tomer you are getting ripped off.
processor is $112 http://www.newegg.com/Product/Product.asp?Item=N82E16819103606
1GB of ram is $82 http://www.newegg.com/Product/Product.asp?Item=N82E16820141307
Case is probally $43
I don't know what mobo he is using so i wount say anything on that
Hard Drive is $40 http://www.newegg.com/Product/Product.asp?Item=N82E16822144102
DVD Burner is $30-$40 http://www.newegg.com/Product/Product.asp?Item=N82E16827101010
should be at least $200 less