Hard disk not found error

guys, my dell inspiron's running on win xp home ed. i recently reinstalled winxp coz the registry was corrupted.

now i have another problem. after a while when the laptop is turned on, the BSOD appears. can't remember the error message but it had the word 'kernel' in it. then when i restart, it says hard disk 0 not found. strike f1 to continue...

 

after a couple of hours, when i turn it on, it boots fine. then after a while, the BSOD comes again. and when i restart i get the same hard disk not found error message. is it some connection problem? should i defragment? hope someone can help. it's getting really annoying especially when im working on something important.

 

thanks in advance