Hello Denise,
The enervating aspect of your situation is also the key point of many television dramas - while there's one symptom, there are many candidates for the cause. Since it is at the core a "signal" issue - that is, does it get there, is it good, is it properly acted upon..., basic signal troubleshooting technniques are apropos. If you have another monitor, or pc, either one will suffice to split the distance: plug the monitor into another pc - no symptoms, the video card is suspect #1. Still symptoms, a loose yoke on the CRT, or a bad flyback transformer (the 2'nd most expensive component in a nonflat monitor, as well as hard to replace, and designed for a functional lifespan of about five years.) Our Poster that notes the low prices of new ones is onto something, if the monitor is at fault. Good luck!
In the evidently likely event that the monitor is at fault, don't even attempt repairs. The high voltages and attendant liabilities ensure that few are qualified, less are insured, and even fewer are inclined to give anyone a fair shake on a repair bill. The Silver Lining of this intermittent cloud is this; A lot of inexpensive, cool running and long lasting flat screens are backwards-compatible.