video card? wich one is better (EDITED) what is Liquid Cooling Technology and how it work?

You should wait until AMD releases their 7000 series! Other than that, 6770 all the way (oh god i love that card <3)

6770 is far better than 6450

the 6770 is miles ahead of the 6450. It's still a decent card but you might want to get something a bit more powerfull if you plan to game on full hd.

6770
Faster GPU, faster memory.

AMD number their cards incrementally unlike nvidia with their 260 being simmilar to the 520, so fked

I really would get a nVidia card, but if you're deciding between the two the 6770 is the obvious choise.

Go to GPUReview to compare the specs

I own the HD6770 1GB DDR5 (migrated from an nVidia 8800GT, since it broke down lately), but I can't be of any help regarding the other card. All I can say is that 6450 has a very inferior memory bandwidth (not to mention pixel and texture fill rates).

What's the power supply of your PSU? Does it have a 6-pin power connector?

Here's a link about Radeon GPU requirements

I'm actually using a 375W Dell Power Supply and haven't encountered any issues (I found some other sites that measured the true amount of total Power needed to use the HD6770 under stress, and 375W was enough... but can't find the link, though)

TL:DR do some research :)

I wouldn't bother with anything less than a HD6850 (or the nVidia equivalent.) The HD6770 is around the same performance as the HD4850 that I've had for 3 years.