What model of camcorder is your video coming from and what format is it?
When you started your project, which project settings did you select? If you selected the proper project settings, then there will NOT be red lines above your clips when you add them to your timeline. Is that the case with your project?
Do you render (press Enter) whenever you add effects and do see red lines above your clips?
Meantime, forget paying some repair shop $200 to fix your computer. You can clean and tune your computer for free using the Deep Care setting on my favorite tune-up tool, Advanced System Care.
Welcome to the forum.
I would start with this ARTICLE, which contains a checklist for getting things to work most smoothly with PrE. It then goes into details on tuning up one's computer and the OS. It finishes with some links to troubleshooting, should everything else fail.
Since things once worked, but quit, the first two things that I would do would be to update the video driver, from the mfgr's. Web site. Next would be the auido driver. If you have a Dell, HP, Lenovo, or other large mfgr's. computer, I would go to their site first, as many tweak the nVidia, or ATI/AMD drivers.
The reason to start there is that even simple OS updates, and hot-fixes, can render those drivers obsolete - what worked fine before, ceases to, after the update. Also, PrE interfaces with both the video and audio driver, much more closely, than almost any other program on your computer, so that everything else can seem to work fine, but when one goes to edit video, things do not work anymore.