Hello, i have a compaq presario S4000NX. After the compaq screen i get a black screen and windows xp does not load up. i have had checksum error messages in the past of 0251 and 0271. I replaced the CMOS battery and everything seemed to be working good for about a week, but now it is happening everytime i turn my computer off. I have to turn my computer off and on about 50 times and finally xp will load. Please Help, Thanks.