Graphics card causing boot problem

Let's clarify one thing. 64 bit system requires much more than 32 bit.

Many users choose, although they have 64 bit motherboard and CPU, to run 32-bit operating system. Why ? Run 32 bit system on a computer that can handle 64 bits is just throwing of time and money.

64-bit components require more computing power. Faster clock speed, faster sending of information and faster delivery of results. In order to achieve all, you need more memory, a wider bus on the motherboard, which confers greater power consumption.

If we look only at the memory. 32-bit operating systems use 2 ^ 32 = 4GB of RAM memory, max! Just look at 64 bit, 2 ^ 40 = 1TB RAM.

It is not difficult to conclude that it takes more energy to operate all components, and much better cooling.

So, just as a precauion, i should minimize gaming unless i get a new PSU as by doing so I'll risk getting my mobo damaged, right? And would 500W be enough?

I agree with your conclusion Your PSU will burn out. Which could damage the components that were working at the time. PSU burning out will free breakdown voltage of 1-2 seconds which can be critical for components on the motherboard. I'm not saying that PSU can burn graphic card or processor, but transistors, capacitors and similar components on the motherboard would probably die. That's a risk.

So, a new PSU is must. Btw, what do you think about that x16 and x1 thing labelled under 'Bus interface' field in GPU-Z? Does that mean that the card was running at it's full potential and the power supply was enough for it but dropped down to x1 when there wasn't enough power for it, and so the fps in games?

It is quite possible. I had a similar problem with my friend's ps, with the graphics like mine. He had little power over 400 watts. When he use a computer more than 10 minutes in a game, computer shut down his game without any prompt for saving, and gets a message on the screen that the power supply is weak, not playable, and that the game can not start with a stronger effect. Game was DarkSiders.

Would lowering the clocks from 600MHz(default) to any low value like 110MHz do any good? I'll give it a try tomorrow.

With that change, you get nothing. You should not decrease speed of your motherboard.

x16 is speed for Graphic transferring between processor and GPU. x16 PCI-express can receive an deliver 4 GB/s (total 8 GB/s in both directions).
What you get if you decrease speed of Motherboard ? Nothing. You will slow down operation of x16 bus..