I am using an Hp compaq6000 pc, recently i discovered while working on the system i often encounter lockup(freeze), especialy when an external device like a flash drive is slot in.What could be the possible caused of this problem?
Unless this is a new machine, I would take a guess on it possibly crashing due to age of machine, and only noticing/coincidence that it happens with USB devices.
Alternatively, Lockups without Bluescreens/similar are usually down to hardware failure - this could be memory/hard drive loosing connection or similar. If you can, check that all cables/connections are in properly and consider reseating the memory.
For the last, it could be inserting a USB stick is jogging the board which causes these problems.
I fear it won't but I hope this helps.
If it is a new machine, all I can suggest is try to update drivers - in particular motherboard/chipset as it is possible you have a dodgy USB controller.