Try taking out the battery, holding the power button for 60 seconds, and putting the battery back in.
RE: Sorry that is not the problem, it is a desktop, there is no battery.
The memory will work in the motherboard, but it will downclock to 800 MHz. Purchasing it would thus be a waste, since the motherboard / processor will not be able to utilize it at it's full speed.
Memory Type: DDR2 PC2-6400, DDR2 PC2-8500, DDR2 (non-ECC)Maximum Memory: 8GBSlots: 4Each memory slot can hold DDR2 PC2-6400, DDR2 PC2-8500 with a maximum of 2GB per slot.