It sounds like there is a hardware incompatibility with those two newer kernels. There is absolutely no disadvantage in staying with a kernel that works well for you. There are not usually any earthshaking improvements in a newer kernel, and there can be cases where functionality for certain hardware functions is dropped as obsolete.
You can always try the next point release when the new kernel updates come in and see if things are working for you again. Otherwise, I would just stay with the 2.6.38.
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