My HP250W 8gb USB pen drive is not detecting only on my Windows OS. But it is detecting on side-by-boot Ubuntu and also on other machines regardless of the OS. Other pen drives also detecting in my Windows. With these facts, I'm pretty sure that there is no complaints in my USB ports and the pen drive.
PS: It stopped detecting in Windows only after I used my pen drive as a bootable Ubuntu installer.
I smell there is something wrong with registry. But couldn't say for sure.