Compatability of Memory Upgrade. I had the Memory stick that came with my Acer Aspire T-180

Question

I had the Memory stick that came with my Acer Aspire T-180 dekstop computer of 512 DDR2 5300 (555mhz) 240 Pin DIMM in the first slot.

I added a 1GB stick of Kybte brand 5300/4200/3200 PC2-667/533/400 240 PIN DIMM (no problems - computer worked fine)

Then I added a generic 1GB stick of PC2-4200 DDR2(533mhz) 240 Pin DIMM (Computer seemed fine for about a month)

Then had the following problems:

1) computer shuts itself off and on quickly at random and slows down considerably to point cannot open word. I replaced my motherboard.

2) When I put the computer back together I had the generic 1GB PC2-4200 stick in first memory slot, the kybte 1GB (5300/4200/3200) stick in the second slot and the factory 512mb (5300) stick in third slot.

Computer seemed to work for a bit and then kept crashing. Reformated entire computer to default factory settings about 5 times then sent back for servicing.

My question: Is it the memory configuration causing my problems or it is a faulty (lemon) computer. I've only had it a few months.

Acer E560 compatibility in memory upgrade