GRUB de GNU

Hola a tod@s,no si es el luegar correcto para postear mi duda, si no lo es ruego me digais dónde he de hacerlo. Tengo un problema con mi distro Precise, bueno la cosa ya venía de cuando tenía instalada la versión Maverick, el caso es que me detectaba un rootkit, que supuestamente alteraba el arranque, modificándolo, a continuación os adjunto la descripción de mi disco hecha con fdisk.
Dispositivo Inicio Comienzo Fin Bloques Id Sistema
/dev/sda1 2048 4098047 2048000 5 Extendida
/dev/sda2 4098048 160352255 78127104 83 Linux
/dev/sda3 * 160352256 332226559 85937152 83 Linux
/dev/sda4 332226560 625141759 146457600 b W95 FAT32
/dev/sda5 4096 4098047 2046976 83 Linux --->Esta es una partición lógica que parte de la extendida

Como podeis ver tengo cuatro particiones principales y una extendida, la primera de las particiones empieza en el sector 2048, esto es traducido a bytes, deja 1 megabyte libre en el principio, la tabla del MBR (primaria y extendida) es la que sigue.

Dispositivo: /dev/sda
0x000: EB 63 90 00 00 00 00 00 00 00 00 00 00 00 00 00
0x010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Aqui empiza el GRUB
0x040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x050: 00 00 00 00 00 00 00 00 00 00 00 80 01 00 00 00
0x060: 00 00 00 00 FF FA 90 90 F6 C2 80 74 05 F6 C2 70
0x070: 74 02 B2 80 EA 79 7C 00 00 31 C0 8E D8 8E D0 BC
0x080: 00 20 FB A0 64 7C 3C FF 74 02 88 C2 52 BB 17 04
0x090: 80 27 03 74 06 BE 88 7D E8 17 01 BE 05 7C B4 41
0x0A0: BB AA 55 CD 13 5A 52 72 3D 81 FB 55 AA 75 37 83
0x0B0: E1 01 74 32 31 C0 89 44 04 40 88 44 FF 89 44 02
0x0C0: C7 04 10 00 66 8B 1E 5C 7C 66 89 5C 08 66 8B 1E
0x0D0: 60 7C 66 89 5C 0C C7 44 06 00 70 B4 42 CD 13 72
0x0E0: 05 BB 00 70 EB 76 B4 08 CD 13 73 0D F6 C2 80 0F
0x0F0: 84 D0 00 BE 93 7D E9 82 00 66 0F B6 C6 88 64 FF
0x100: 40 66 89 44 04 0F B6 D1 C1 E2 02 88 E8 88 F4 40
0x110: 89 44 08 0F B6 C2 C0 E8 02 66 89 04 66 A1 60 7C
0x120: 66 09 C0 75 4E 66 A1 5C 7C 66 31 D2 66 F7 34 88
0x130: D1 31 D2 66 F7 74 04 3B 44 08 7D 37 FE C1 88 C5
0x140: 30 C0 C1 E8 02 08 C1 88 D0 5A 88 C6 BB 00 70 8E
0x150: C3 31 DB B8 01 02 CD 13 72 1E 8C C3 60 1E B9 00
0x160: 01 8E DB 31 F6 BF 00 80 8E C6 FC F3 A5 1F 61 FF
0x170: 26 5A 7C BE 8E 7D EB 03 BE 9D 7D E8 34 00 BE A2
0x180: 7D E8 2E 00 CD 18 EB FE 47 52 55 42 20 00 47 65
0x190: 6F 6D 00 48 61 72 64 20 44 69 73 6B 00 52 65 61
0x1A0: 64 00 20 45 72 72 6F 72 0D 0A 00 BB 01 00 B4 0E
0x1B0: CD 10 AC 3C 00 75 F4 C3 00 00 00 00 00 00 00 20
0x1C0: 21 00 05 17 18 FF 00 08 00 00 00 80 3E 00 00 17
0x1D0: 19 FF 83 FE FF FF 00 88 3E 00 00 40 50 09 80 FE
0x1E0: FF FF 83 FE FF FF 00 C8 8E 09 00 98 3E 0A 00 FE
0x1F0: FF FF 0B FE FF FF 00 60 CD 13 00 88 75 11 55 AA

Tablas de la particion extendida
0x000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x110: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x120: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x130: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x140: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x150: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x160: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x170: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x190: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x1A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x1B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 41
0x1C0: 02 00 82 17 18 FF 00 08 00 00 00 78 3E 00 00 00
0x1D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x1E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x1F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA

Tecnicamente los primeros 63 bytes de la tabla deberían estar a 0, pero si los pongo (con el comando dd), la máquina no arranca, tampoco arranca si pongo a cero el espacio que hay entre los MBR y la primera partición. Me inquietan los primeros 3 bytes del MBR, pero desconozco si deben estar así.

¿Alguien me podrÃa explicar que es lo que esta pasando?, creo que lo he probado todo y nada, el efecto continúa. Tampoco tendo un sistema de referencia para determinar si lo tengo correcto o no, si alguien tiene un sistema que esta seguro de no ser corrupto, le agradecerí que me enviara su descripción del MBR (fdisk, opción x, opción d).
Gracias anticipadas por vuestra ayuda..