Well my PC spec are as follows 4gb ram nvida 240 gt graphics card and and 64 athlon x2 dual.core processor
Ahhh, hunni.
Your specs are low.
I don't want to sound shitty but the 240 gt was entry level when it launched and that was over a decade ago. I don't think you have the power to be running a lot of Unity games.
That GPU came out towards the end of 2009 so you're like 10 years behind on specs.
I don't think there is any way of getting them to run on that system.
I don't want to go and say upgrade your system, I know that's not possible for everyone but if at all possible I would keep my eyes open for a cheap low end system with some more up to date components.
I don't know where you live or your financial situation so can't comment on that but if you do want to run games requiring more power you may have to think about saving for an upgrade or seeing if any conversions to easier to handle engines happen.
Some VN's do get moved over to Ren'py every so often.