Many commands aren't working in Solaris 5.9

Hello,

We've a Solaris 5.9 machine running in production. All of a sudden, many of the commands are stopped working but few commands like uname, ps, pwd, prtconf are working.
Whenever I execute commands like ls, cp, swap...it throws the error "Illegal Instruction" and whenever I execute commands like metastat, bash, env...it says "cannot execute"  and when i execute "format", it says "Killed".

Not sure what has happened. Please let me know how to fix this issue.

Thanks,
Ash
 

$ su - root
su: u\242\372\200^G\201$^A^B^B^Q\3648P^_\3038P^_\303H]^YF^L^_\347^]f\260: execute permission denied
su: ^C_^B^Bu\242\373\200^G\201$^A^B^B^R\3528P^_\3038P^_\303H]^YF^L^_\347^]f\270: execute permission denied
su: 3~\252\251^B^Bu\242\372\200\200^G\201$^A^B^B^O\3608P^_\3038P^_\303H]^YF^L^_\347^]f\254^HF: execute permission denied
su: syntax error at line 3: `m_\207\205^B^Bu\242\373\200\200^G\201$^A^B^B^Q\3678P^_\3038P^_\303H]^YF^L^_\347^]g\360' unexpected
$

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