I've recently bought a Cisco 2500 to test with off of an online auction site. The first 2 days I had it powered on and did some basic config on it and everything was fine. I left it powered on over the weekend and when I checked it on Monday I noticed that it had (boot) next to the hostname. I checked the IOS file in flash and it had an [invalid checksum] next to it. I've tried erasing the flash and copying the IOS file over again via tftp and even though it seems to copy over fine(the size of the file in flash is the same as the original), it fails the checksum verification and still has [invalid checksum] so the router isn't booting properly. I don't have other flash memory to test whether the problem is a hardware one but is there something else I can try? Did I just buy a dud?