Help with upgrades on older PC

Hello!

I had a PC built by DS in late 2010. I've enjoyed many great years with this PC, but sadly the video card has stopped working. I'd like to save up to buy a more current PC from DS, but in the meantime, I need to extend the life of this PC for another year or two through a video card replacement/upgrade and possibly other small upgrades like RAM. Money is tight at the moment, so my budget is very limited. I'm trying to determine what performance upgrades can be done for around $100-$150 (wishful thinking?). I've primarily used this PC for entertainment (gaming, video streaming, heavy internet usage), but I'll also now be using it for work (word processing, clerical). Unfortunately, I'm pretty clueless and easily confused when it comes the inner workings of a computer and selecting appropriate computer parts. I remember how helpful everyone here was when I ordered my DS PC, and I'm hopeful to get some assistance from you fine folks again! I've copied my DS PC specs at the bottom of this post for reference.

Video card:
I was a bit disheartened to see that the cost of some older video cards is quite high (like the GTX 580 in my PC). It seems that upgrading from the GTX 580 would be more cost efficient, but determining the best video card for my PC specs and usage has left me stumped. Any suggestions for a video card upgrade (Nvidia preferred) from the GTX 580 that can support a dual monitor setup?

RAM:
My PC has 6GB of RAM, and system performance has become more sluggish over time. I'm not sure how to figure out what additional RAM could improve system performance, while not being "overkill". Also, what is the recommended way to go about purchasing a RAM upgrade - i.e., add additional RAM to my existing RAM or replace/upgrade my existing RAM entirely? From what I can see on my motherboard, the RAM in my PC is in a 2GB x 3 setup, and I believe there are 6 RAM slots total.

Honestly, I'm not sure how much upgrading is even possible or worthwhile given my limited budget and the age of the PC itself, but I'm open to suggestions. At the very least, I need to replace the non-functioning video card. Any help you can provide would be greatly appreciated. Thank you so much for your time.


My DS PC specs:

Config ID:
DSO­253692
Chassis Model: Special Deal Hot Seller ­ Black OPS Assassin Edition
Processor: Intel Core i7 950 3.06GHz (Quad Core)
Motherboard: EVGA X58 SLI 3 Edition (USB 3.0 & SATA 6Gb/s) (Model: 131­GT­E767)
System Memory: 6GB DDR3 1600MHz Digital Storm Certified Performance Series (Highly Recommended) (Hand Tested)
Power Supply: 1200W Corsair Pro Gold Series (CMPSU­1200AX) (Dual/Triple/Quad SLI Compatible)
Hard Drive Set 1: Operating System: 1x (160GB Solid State (By: Intel) (Model: X25­M MLC Edition) (Extreme
Performance)
Hard Drive Set 2: Multimedia\Data: 1x (1TB Western Digital Caviar (7200 RPM) (64MB Cache) (Model: Black Edition
WD1002FAEX)
Optical Drive 1: DVD­R/RW/CD­R/RW (DVD Writer 24x / CD­Writer 48x) (LightScribe Edition)
Optical Drive 2: Blu­Ray Player/DVD Player (Play Blu­Ray and Play DVDs)
Internet Access: High Speed Network Port (Supports High­Speed Cable / DSL / Network Connections)
Video Card(s): 1x NVIDIA GeForce GTX 580 1.5GB (Includes PhysX Technology)
Sound Card: Creative Labs X­Fi Titanium Fatal1ty Professional (PCI­Express Slot Based)
Extreme Cooling: AIR: Stage 1: Noctua NH­U12P SE Dual 120mm Fans High Performance Cooler
CPU Boost: FREE: Stage 1: Overclock the processor between 3.3GHz to 3.9GHz (Cooling Upgrade Recommended)
Windows OS: Microsoft Windows 7 Home Premium (64­Bit Edition)