Video Card Problems/Dell optiplex 755
I want to add graphic card to my desktop with processor E6850(3 GHZ). I want to add 2 gb graphic card to play games like tekken 6, kindly guide me which model graphic card I should add and which company graphic card.
Dell documentation lists multiple versions of the Optiplex 755, the primary difference being enclosure size. Which version of the 755 you have will influence the kinds of add-in cards you can install.
If you have the mini-tower version, your system supports a full-height PCIe x16 graphics card, and is only limited by the system's 305W power supply (which will restrict you to lower-power graphics cards); the other two versions (slim tower and desktop) both feature half-height expansion capabilities, due to the smaller size of the enclosure. They also feature slightly smaller power supplies (275W). If you happen to have the "ultra small form factor" variation, expansion is not possible.
See this page for differences between the models:
Within the restrictions of a ~300W power supply, you still have a number of options as entry-level to mid-range cards from both AMD and nVidia (both are good choices). For example the Radeon HD 5400 and 6400 series should be acceptable choices, and will provide better 3D performance over an IGP (integrated graphics). However, do keep in mind that if you have a large number of peripherals that draw power from the machine, you may run into some issues (e.g. if you have a lot of hard drives). Unfortunately Dell systems tend to use proprietary power supplies, so upgrading the power supply is generally not an option in your situation. It should also be noted that the memory size of a given graphics adapter is not the sole determinant of its performance - the chipset used also matters. When looking for an upgrade, look for the newest compatible hardware you can find (e.g. Radeon 6000 series is newer than Radeon 4000 series) as it will generally mean better performance, even if both cards have the same amount of memory.
However, while you can upgrade the graphics adapter for your computer, the game you specifically mentioned (Tekken 6) is not available for the PC platform. It is only available for PlayStation 3, PlayStation Portable, or Xbox360. In order to play this title, you would need a supported game console (and in general I would suggest a game console to those looking to game on a budget, or with a computer that is not substantially upgradable (such as yours), as it will be much more economical than replacing an entire desktop computer).