Need Help Upgrading Dell Precision T3400!

the parts you picked are way overpriced. the Dell case is somewhat proprietary, so the MB probably won' t fit. you need to get a new case. the PSU you chose is terrible also. here is was I would do.

reuse your DVD and HDD (use the HDD as secondary storage)

buy:

Case (place holder. pick any case you like)
COOLER MASTER Elite 430 RC-430-KWN1 Black Steel / Plastic Computer Case
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$10.00 Mail-in Rebate
$49.99
PSU
SeaSonic M12II 620 Bronze 620W ATX12V V2.3 / EPS 12V V2.91 SLI Ready 80 PLUS BRONZE Certified Modular Active PFC Power Supply
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$89.99
MB
GIGABYTE GA-Z77MX-D3H LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 Micro ATX Intel Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$129.99
CPU
Intel Core i5-2500K Sandy Bridge 3.3GHz (3.7GHz Turbo Boost) LGA 1155 95W Quad-Core Desktop Processor
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$204.99
RAM
Crucial Ballistix sport 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model BLS2KIT4G3D1609DS1S00
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$40.99
GPU
EVGA 02G-P4-3660-KR GeForce GTX 660 Ti 2GB 192-bit GDDR5 PCI Express 3.0 x16 HDCP Ready SLI Support Video Card
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$299.99
SSD (use as you boot drive and apps drive)
Kingston HyperX 3K SH103S3/120G 2.5" 120GB SATA III MLC Internal Solid State Drive (SSD) (Stand-Alone Drive)
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
$99.99
--------
$915.93 + $7.33 Shipping = $923.26

I would really like to know if it will fit. I really like the case I have. It means alot to me. and im on a budget.

It's a BTX case, can't use an ATX motherboard

there's your answer ^

if you are on that tight a budget why a $300 GPU?

dropping the SSD out of my build puts you under what you were originally going to spend including the case.

Im a hardcore computer gamer. I wanna play games like BattleField 3 and skyrim and such games what video card is best to fit that I would like Nvidia.

I understand. in that case you should think about the GTX 660. less money and performance is within 4FPS usually.
http://www.tomshardware.com/reviews/geforce-gtx-660-gef...

EVGA already has a super clocked edition out. its $80 less and free shipping
http://www.newegg.com/Product/Product.aspx?Item=N82E168...