Yes, I fear that your TiBook has developed a problem with the BGA joints under the graphics chip. This problem is unfortunately widespread (the early iBooks were infamously prone to early failure, but other models have suffered from this problem as well).

Some folks have used shims to put pressure on the chip. It helps a bit, but it's not a long-term solution. Others have attempted to reflow the joints using a heat gun. If you get to a point where the machine is useless, you might be tempted to give that a go.