XP can't boot or recover

[Vicky12]

We have 4 PCs at home: one Win7, one Vista, one PX Home, and one XP Pro.
Two of them get the same problems at the same time.
The things these two PCs have in common:
1. Windows XP operating system.
2. Often browsing Youtube, facebook, school websites and so on.


Ages of these two PCs:
Desktop, 7 years, XP Pro sp2 32b. w/Malwarebytes free & Avira free.
Laptop, 3 years, XP Home sp3 32b. w/Malwarebytes free & Avira free.


Situations of the problems:
Phase One:
Often crashing.
Phase Two:
Sometimes not boot, not recover; other times everything all right.
Phase three:
...hal.dll...missing or corrupted....
...ntldr...missing or corrupted....
No drive attached ... BIOS is not installed....
...safe mode...start normally...menu
If safe mode was selected, PC shut down after 4-5 minutes.
If start normally was selected, Welcome and then BSoD after 4-5 minutes.
At this stage,
Hot keys of recovery not functioning.
Hot key of safe mode not functioning.
Any changes in BIOS not effective.
BIOS recognized HDD.

How to eleminate the problem, please?

Thanks.
Vicky

 

[office politics]

i would prolly complete these steps one at a time.

update bios on mobo

run memtest86 overnight. random unexpected errors can be caused by bad memory.

run hard drive diags from manufacturer.

reinstall windows

start replacing parts