I bought a computer back in 2007 and just recently took off the heatsink fan to clean it, omg there was so much dust in the heatsink. Like clumps of it... the heatsink is attached to the motherboard by screws. anyways i noticed the thermal paste was dried up and i have no idea how long it has been like that. But my cpu never shut down from overheating or anything and it still works. the cpu is a q6600. Should I reapply thermal stuff or is it supposed to be dry?
Definitely clean off the CPU and heatsink and reapply fresh thermal compound.
Some compounds, like Arctic Silver, cure over time and do lose some of their moisture, but if you break the seal between heatsink and processor, cured compound will no longer be able to conduct heat well, and you must start over with clean surfaces and fresh compound.