Why can't my PC run litecoin mining programs?

Uninstall all your drivers, reboot and do a fresh install. After that look for the OPENCL drivers and install
those.

Make sure you download GUIMINER from a reputable place, i've seen allot of infected GUIMINER.

Your card is supported and should mine at about 390/400k. Decent.

The reason your screen goes blank and starts up again might be due to your GUIMINER settings.
You might need to tweak them. Did you try loading the GUIMINER defaults for your card? If you did that
and it still bugs out, search the web to see setting others used.

Another tip, make sure your fans are all working and that airflow is maximized to avoid heating up your card.
I also recommend you install a software that monitors the GPU and CPU heat and keep it under 80 celcius
at all times.

I've been getting about $10/week+ mining Litecoin and playing the market. I mine litecoin 1 day and then
a smaller coin 1day. Building my portfolio.

You should try to look for a driver that supports the software or an update. In any case, I hope you didn't spend money on that BitCoin mining program, BE CAREFUL OF SCAMS!!!! You might want to just delte it altogether and look for some other kind of software altogether. It could be a virus! But with any luck it was just poorly coded.