No hard drive?

I have windows xp, with two sata2 hard drives installed, one contains
recovery and operating sytem and the other for backup/data storage. until
recently both these worked fine.
however now when i boot my pc it sees the backup hdd in BIOS, but when it
boots it takes about 10minutes to clear the windows logo screen and the drive
is not seen by explorer or any other program . ran SMARTcheck from BIOS but
was ok. i tried safe mode and the drives showed up and worked fine, tried
restore but it was blank.
i think i made a booboo by downloading some awful program tweakxp i think it
was.
however this also roughly coincided with an upgrade from avg 7.5-to avg8.
please help me get them back surely it's something simple.