Question about problem recently built computer

I recently ordered the components and built a computer from Scan, it was my first experience with the company and I have to say I am very pleased, delivery was prompt as was customer services help with changing some items.

I am pretty sure that I know what this problem is, and I feel like a bit of a fool, but this is the first time I have built a PC since my athlon XP 1700+ rig "back in the day". I know i'm responsible for any and all problems with the PC and just hoping to get some advice :).

The PC component list is as follows:

Core 2 Duo E6420
Gigabyte GA-965GM-S2 Mobo
Corsair TWIN XMS 2GB 4-4-4-12 PC6400 RAM
Samsung 500GB 7200rpm HDD
DVDR/W Drive
X1950GT 512MB
VIsta Home Premium

The PSU powering this is 400w, which I think is the problem as I think it is below what is needed to power all these component properly. I have ordered a 700w XClio PSU which I forgot to order originally, and it should hopefully be here tomorrow, but I just wondered if anyone could confirm that this is a PSU related problem:

The PC runs vista fine, it recognises the card as I have installed the catalyst drivers, and also runs aero, no graphical anomalies or problems at all. The problem is when a game loads up, as soon as any kind of 3D graphics is displayed the screen froze, with multicoloured artifacting/lines/marks on the screen and the PC stopped responding.

I only tried launching a game twice, as if it is a PSU problem its not something I want to keep recreating! The first time was with Star Wars Empire at War and yielded the aformentioned result, the second time was with Homeworld 2 which initially claimed that the card was an "incompatible radeon card" and ran for a second before producing the same result.

Does sound like an underpowered PSU meaning there's not enough power to the Gfx card. Only problem is you can actually damage the cards doing this sometimes...

see if you can borrow a psu off a friend and id say you should be looking for 500w minimum

If youre buying id get a corsair 520w Best value psu ever and will work a treat with your setup :)

With the specifications stated a 400 Watt Power Supply could be sufficient to run all the components depending on the manufacturer and quality of the unit. A good quality branded PSU (i.e. Enermax, Antec etc) can run above it's rated wattage for a couple of minutes. Although it should be stated that ATI recommend that a minimum of a 450 watt PSU for their X1950GT 512MB with an 28 - 30 amp on a 12 volt line.

A good indication of power useage can be found here:

www.extreme.outervision.com/psucalculator.jsp

Before ordering a brand new PSU it might be advisable to eliminate other plausible reasons for the crash. Currently there are a number of stability issues with the ATi X1950GT / XT series with the Vista Operating System from drivers, to a physical overheating problems. Try uninstalling the catalyst 7.1 - 7.3 drivers, and use the pre-installed drivers that come with Vista. Also make sure there is sufficient cooling for the system, as artifacting and freezing is indicative of a overheating problem.