If it's a power supply issue (likely) don't waste your money on a new PSU, there are plenty of refurbished Dell desktop boxes on ebay. We bought 5 for work all under $400 for i7 with 8g ram and all with W7 pro licences and W10 upgrade pre-loaded. Also capable of running dual monitors with an additional display port adapter $20 from the same buyer.
http://www.ebay.com.au/itm/Dell-Opti...YAAOSwOgdYp3Hd