PC hangs while playing a certain game

Heat issue? Have you checked to make sure ALL your fans are properly connected and spinning. Free of fluff and cat hair with plenty of case ventilation?

Drivers...this is a beta so drivers could be an issue.

What OS are you using?

I would consider the fact that your RAM is from another machine. Not that the Dell RAM is bad, but it might not be compatible. To test your RAM, run memtest86+ for a few hours to see if you get any errors. If you do, then you might want to consider buying compatible RAM.

Did you download the most recent drivers for your graphics card, or just use the CD? I would install the latest, if you haven't already. A BETA game has a much higher chance of crashing than an RTM game, obviously, but newer drivers may have fixes for BETA titles as well.

As previously mentioned, make sure your cooling is working as expected. You may want to monitor CPU temps under load using Prime95 and CoreTemp, and make sure your CPU heatsink is on tight.

I would start with RAM on this one.

to both of you I am using windows 7 64 bit and I only have one case fan and I have noticed that after opening my machine after the crashes the ram is extremely hot i previously had some 1600mhz corsair dominator memory but they were faulty the temps for the gfx card ar around 40-60 c and reaching 65 in graphicly intensive games i have also monitored the cpu temps and they are around 56c while in heavy gaming I have ordered and extra fan and I am getting new ram as a replacement of my faulty dominator's they are : G-skill 1600mhz 4gb. one last thing i am getting this problem when i am running my computer for lets say 30 mins the first freeze happens and then i restart and play a game then every 2-3 mins a freeze will happen i am also using the 11.10 beta drivers off amd and the airflow is ok in my case the case temps are around 40-50c and about 30 idle

Like leo2kp said, run memtest86 too.

I ran it and it came up with no errors

play bf3 on another window........like on win 7 or on xp.

I am using win 7 and bf3 is not compatible with xp...

to all i have figured it out it was psu failure as my computer has started shutting down while playing any games or gpu/cpu heavy applications and i have asked for a refund on the psu and will be getting a different more powerful one