Multicurreny issue

Multicurrency not working

1. Base shop is in INDIA. Default currency is INR.
2. When Tried from USA , the currency shows as USD.

Now the issue is

1. When i Access the price from UK (London), the price becomes in INR, instead of USD. How do i solve this.
2. Also the price changes to Indian Value.
3. Need to fix a same Price in USD across all countries except INDIA. (One Price, One currency Across world, other than INDIA)