Hatwan :
my cpu its i3 4150 3.50ghz ram 4gb ddr3 1600mhz psu dell 290watt 80bronze 750gb HDD
Sorry I was away for so long. I don't feel that my above response solved the question so I ask either OP or a moderator (whichever gets to it first) to unselect it for me.
The PSU in that model is terrible. I would be happier trying to power my computer with an actual potato because at least a potato can't take a crap and send a surge through my system. Ready for the punch line? Dell = Deplorable Equipment & LackLusture.
Sorry, I had to.
As stated by bignastyid (nice name BTW I love it), your motherboard uses that proprietary connector that Dell just loves to force down our throats. The products sold by Mod DIY are worlds above the other thin gauge wire crap you'll find online. It's well worth the $15 if the other option is the possible destruction of your system, right?
Here's what you're looking at to get your system ready for a $100 graphics card:
1) $15 for a power adapter because Dell
2) At least $35 for a new power supply because Dell
Effectively, you're spending $50 to get ready for a $100 graphics upgrade. Are you sure you want to spend this kind of money on your current machine?
Here's a better question that I'm really surprised hasn't been asked yet: Do you have the wider tower or the slim one? The slim one needs a special size expansion bracked and probably different sized power supply as well.
Refer to this page for pictures of the two variants.
Trying to upgrade a slim is like trying to make a chocolate milkshake out of raspberry potatoes. Dell, slim and upgrade just don't belong together, just like how raspberry, potatoes and chocolate just don't belong together.