If you would know the age of this pc you would immediatly throw him out of the window, believe me. Its definitly better to buy a new one instead of feeding a dead thing with money.
At moment i use my tv as screen with s-Video, im sure the grafic card is making the Crashs, with s-Video i have a better Chance to copy my important stuff on extern Drives. S-Video is also using the grafic card, i Know, but i think the Crash comes from where i put the Monitor in. (dunno english word) (Output? Cable? / you Know what i mean)
CPU and mainboard also Making Problems, Big restart Problems, at least 5 restart before it starts, so i have to be fast with copying.
Maybe you didn't catch my drift, so I'll make it a little clear for you.
You are better off buying the custom computer parts SEPARATELY, rather than splurging on the branded pc. They don't gives you a good benefits on upgrades ( Not always, actually )
So, financially speaking, you could reuse some of what you already had, such as case, hard drive, cd burners?
At my understanding is that you uses the S-Video to hook up to the TV, which it's old technology.
I'm not sure if your monitor are capable to support the few of inputs, such as DVI-D, Composite ( HDTV of red, green and blue cables ), or HDMI ?
It would be really easy for yourself to buy the basic parts that suits to your needs, like, you don't really the big, muthafucking GTX295 to run for just a stupid HL2DM, that would waste a lot of your money, right?
So try and aim on low to mid-end computers, such as Intel Core 2 Duo ( it's fast and cheap, i have E7300 and never had problems with it )
Now, did you catch my drift, or do I have to order a bananas split buttseck specials for you?

By the way, when you get the new pc, you can plug your old hard drive in, and transfer all of your old datas, and you could reuse your old hard drive from that point.
Edited:
You can start off by getting the barebone, and spending the small upgrades from that point.