i have an ATI Radeon HD5670 GDDR5 1GB... but Windows 7 only recognizes 700mb.
I installed the latest drivers from AMD's web site, but it doesn't work.
What can I do?
I think that is actually the amount of shared memory from the system, at least in some form, partially. I have a 128MB card, yet it reports 1405MB (I would assume that your number is much lower because it does not need to borrow as much memory from the system as you have a lot more on your card than I do). If you Google "dxdiag video memory" (minus the quotes), you will find that virtually no one reports that figure equaling their actual video memory.
In other words, I don't think you have an actual problem.
This is for Vista, but probably relevant to Windows 7 also:
Try using this Windows-integrated tool instead: